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Title:
CORE-SHELL PARTICLES
Document Type and Number:
WIPO Patent Application WO/2019/218027
Kind Code:
A1
Abstract:
The application relates to a core-shell particle having a) a cross-linked polyelectrolyte core, and b) a silica-based shell having covalently bound thereto one or more groups of formula –R–F, wherein R is an organic group and F is a functional moiety. The application also relates to a method of synthesis of a core-shell particle, the method comprising the steps of: a) providing a cross-linked polyelectrolyte core template, b) coating the core template with a silica-based shell, and c) introducing one or more groups of formula –R–F covalently bound to the silica-based shell, wherein R is an organic group and F is a functional moiety.

Inventors:
MEANEY SHANE (AU)
TABOR RICHARD (AU)
FOLLINK BART (AU)
Application Number:
PCT/AU2019/050475
Publication Date:
November 21, 2019
Filing Date:
May 17, 2019
Export Citation:
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Assignee:
UNIV MONASH (AU)
International Classes:
B01J13/02; A01N25/10; A01N25/26; A61K9/50; B01J21/08; B01J23/00; B09C1/08; C01B33/149; C08J3/24; C08J7/04; C08L33/02; C08L33/26; C08L77/00; C08L79/00; C08L81/00
Foreign References:
US20170110625A12017-04-20
KR20170035721A2017-03-31
US20120292572A12012-11-22
US20110274832A12011-11-10
JP2018035031A2018-03-08
Other References:
GORYACHEVA, O A ET AL.: "Modification of polyelectrolyte microcapsules into a container for the low molecular weight compounds", PROC. SPIE 10716, SARATOV FALL MEETING 2017: OPTICAL TECHNOLOGIES IN BIOPHYSICS AND MEDICINE XIX, vol. 10716, 26 April 2018 (2018-04-26), XP060102525
MEANEY, S P ET AL.: "Synthesis, Characterization, and Applications of Polymer-Silica Core-Shell Microparticle Capsules", ACS APPL. MATER. INTERFACES, vol. 10, no. 49, 2018, pages 43068 - 43079, XP055654043
Attorney, Agent or Firm:
DAVIES COLLISON CAVE PTY LTD (AU)
Download PDF:
Claims:
THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS

1. A core-shell particle having:

a) a cross-linked polyelectrolyte core, and

b) a silica-based shell having covalently bound thereto one or more groups of formula -R-F, wherein R is an organic group and F is a functional moiety.

2. The particle of claim 1, wherein the poly electrolyte is selected from poly(acrylamide), poly(acrylic acid), poly(allylamine), poly(ethylenimide), poly(styrene sulfonate), poly(N-isopropylacrylamide), poly(diallyldimethylammonium chloride), and a combination thereof.

3. The particle of claim 1 or 2, wherein R is selected from an alkyl group, an alkenyl group, an aryl group, and a carbocyclyl group.

4. The particle of any one of claims 1-3, wherein F is selected from a hydroxyl group, an amino acid group, an amide group, an amine group, an imide group, a thiol group, a phosphate group, an epoxy group, an alkyl halide group, an isocyanate group, a hydrazide group, a semicarbazide group, an azide group, an ester group, a carboxylic acid group, an aldehyde group, a ketone group, a disulfide group, a xanthate group, a thiocyanate group, and a thiosulfate group.

5. The particle of any one of claims 1-4, wherein the cross-linked polyelectrolyte core comprises a core additive selected from a nanoparticle, a microparticle, a bio-molecule, an ionic species, a cell, and a combination thereof.

6. The particle of any one of claims 1-5, wherein the silica-based shell comprises a shell additive coordinated to the functional moiety, the shell additive being selected from a nanoparticle, a microparticle, a bio-molecule, and a combination thereof.

7. The particle of claim 5 or 6, wherein the nanoparticle is selected from a gold nanoparticle, a magnetite nanoparticle, a Quantum Dot, and a combination thereof.

8. The particle of claim 5 or 6, wherein the bio-molecule is selected from an amino acid, a protein, a nucleic acid, and a combination thereof.

9. The particle of claim 5 or 6, wherein the ionic species is selected from a potassium ion, a nitrogen-containing ion, a phosphorous-containing ion, a sulfur-containing ion, a iodide ion, an ion of a transition metal belonging to the d-block of the Chemical Periodic Table, an ion of a lanthanide belonging to the f-block of the Chemical Periodic Table, an ion of an alkaline earth metal belonging to the s -block of the Chemical Periodic Table, and a combination thereof.

10. The particle of any one of claims 1-9, wherein the silica-based shell is directly attached to the cross-linked polyelectrolyte core.

11. A method of synthesis of a core-shell particle, the method comprising the steps of: a) providing a cross-linked polyelectrolyte core template,

b) coating the core template with a silica-based shell, and

c) introducing one or more groups of formula -R-F covalently bound to the silica- based shell, wherein R is an organic group and F is a functional moiety.

12. The method of claim 11, wherein the poly electrolyte is selected from poly(acrylamide), poly(acrylic acid), poly(allylamine), poly(ethylenimide), poly(styrene sulfonate), poly(N-isopropylacrylamide), poly(diallyldimethylammonium chloride), and a combination thereof.

13. The method of claim 11 or 12, wherein the step of providing a cross-linked polyelectrolyte core template comprises exposing the polyelectrolyte to a cross-linking agent selected from N,N’-methylenebisacrylamide, epichlorohydrin, bis(2- methacryloyl)oxyethyl disulphide, l,4-bis(4-vinylphenoxy)butane, divinylbenzene, p- divinylbenzene, glycerol ethoxylate, glycerol ethoxylate-co-propoxylate, hexa(ethylene glycol) dithiol, 2-[8-(3-hexyl-2,6-dioctylcyclohexyl)octyl]pyromellitic diimide oligomer, 2-[8-(3-hexyl-2,6-dioctylcyclohexyl)octyl] pyromellitic diimide oligomer, 11- maleimidoundecanoic acid, pentaerythritol ethoxylate, pentaerythritol ethoxylate, pentaerythritol propoxylate, l,4-phenylenediacryloyl, poly(ethylene glycol) bisazide, poly(ethylene glycol) diacrylate 2,4,6,8-tetramethyl-2,4,6,8-tetrakis(propyl glycidyl ether)cyclotetrasiloxane, l,3,5-triallyl-l,3,5-triazine-2,4,6(lh,3h,5h)-trione, triethylene glycol dimethacrylate trimethylolpropane ethoxylate, trimethylolpropane ethoxylate, trimethylolpropane ethoxylate 4-vinylbenzocyclobutene, and a combination thereof.

14. The method of any one of claims 11-13, wherein R is selected from an alkyl group, an alkenyl group, an aryl group, and a carbocyclyl group.

15. The method of any one of claims 11-14, wherein F is selected from a hydroxyl group, an amino acid group, an amide group, an amine group, an imide group, a thiol group, a phosphate group, an epoxy group, an alkyl halide group, an isocyanate group, a hydrazide group, a semicarbazide group, an azide group, an ester group, a carboxylic acid group, an aldehyde group, a ketone group, a disulfide group, a xanthate group, a thiocyanate group, or a thiosulfate group.

16. The method of any one of claims 11-15, wherein the coating of the core template is effected by promoting hydrolysis and condensation reactions of alkoxysilanes and functional alkoxysilanes.

17. The method of claim 16, wherein:

(i) the alkoxysilanes are selected from methyltriethoxysilane (MTES), phenyltriethoxysilane (PTES), diethyldiethoxysilane, methyltrimethoxysilane (MTMS), dimethyldimethoxysilane, phenyltrimethoxysilane (PTMS), vinyltrimethoxysilane (VTMS), vinylriethoxysilane (VTES), tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), tetrapropoxysilane (TPOS), tetrabutoxysilane (TBOS), and a combination thereof, and

(ii) the functional alkoxysilanes are selected from 3-aminopropyl triethoxy silane, 3- aminopropyl trimethoxysilane, 3-isocyanatopropyl triethoxysilane, 3-isocyanatopropyl trimethoxysilane, 3-azidopropyl triethoxysilane, 3-azidopropyl trimethoxysilane, 3- thiolpropyl trimethoxysilane (or 3-mercaptopropyl trimethoxysilane or trimethoxysilyl propanethiol), 3-thiolpropyl triethoxysilane (or 3-mercaptopropyl triethoxysilane or triethoxy silyl propanethiol), 3-cyanopropyl trimethoxysilane, 3-cyanopropyl triethoxysilane, N-(2-aminoethyl)-3-aminopropyl trimethoxysilane, N-(2-aminoethyl)-3- aminopropyl triethoxysilane, (aminoethylaminomethyl) phenethyl trimethoxysilane, (3- acetamidopropyl) trimethoxysilane, acetoxyethyl trimethoxysilane, 3-acrylamidopropyl trimethoxysilane, acryloxymethyl trimethoxysilane 3-bromopropyl trimethoxysilane, 3- chloropropyl trimethoxysilane, (heptadecafluoro- 1 , 1 ,2,2-tetrahydrodecyl) trimethoxysilane, (heptadecafluoro- 1,1, 2, 2-tetrahydrodecyl) triethoxysilane, 2-

[methoxy(polyethyleneoxy)2i-24propyl]trimethoxysilane, and a combination thereof.

18. The method of any one of claims 11-17, wherein step a) further comprises adding a core additive to the polyelectrolyte, the core additive being selected from a nanoparticle, a microparticle, a bio-molecule, an ionic species, a cell, and a combination thereof.

19. The method of any one of claims 11-18, further comprising coordinating a shell additive to the functional moiety, the shell additive being selected from a nanoparticle, a microparticle, a bio-molecule, and a combination thereof.

20. The method of claim 18 or 19, wherein the nanoparticle is selected from a gold nanoparticle, a magnetite nanoparticle, a Quantum Dot, and a combination thereof.

21. The method of claim 18 or 19, wherein the bio-molecule is selected from an amino acid, a protein, a nucleic acid, and a combination thereof.

22. The method of claim 18 or 19, wherein the ionic species is selected from a potassium ion, a nitrogen-containing ion, a phosphorous-containing ion, a sulfur- containing ion, a iodide ion, an ion of a transition metal belonging to the d-block of the Chemical Periodic Table, an ion of a lanthanide belonging to the f-block of the Chemical Periodic Table, an ion of an alkaline earth metal belonging to the s -block of the Chemical Periodic Table, and a combination thereof.

23. The method of any one of claims 11-22, wherein the silica-based shell is coated directly to the cross-linked polyelectrolyte core.

Description:
CORE-SHELL PARTICLES

FIELD OF THE INVENTION

The present invention relates generally to core-shell particles, and in particular to a polyelectrolyte polymer- silica core-shell particle and a method for preparing the same.

BACKGROUND OF THE INVENTION

Polyelectrolyte polymer- silica composites are an important class of materials with applications in sensors, self-healing, and coatings. The presence of distinct organic and inorganic phases provides complementary physiochemical properties. Silica typically provides a solid, inert substrate with improved resistance to thermal, chemical, and mechanical damage when compared to bare polymer phases. The polyelectrolyte polymer conversely offers a wealth of possible chemical environments and opens manifold avenues for tailoring the function of the material.

When in particulate form, polyelectrolyte polymer- silica composites offer potentially new application avenues in fields such as agriculture, fluid purification, and drug-delivery.

While there have been successful attempts to synthesise polyelectrolyte polymer- silica composite particles, in most cases those attempts resulted in composite organic-inorganic hybrid particles in which the inorganic phase is homogeneously dispersed throughout the organic phase. This inherently limits the synergistic combination between the physical and chemical stability offered by the silica and the highly customisable chemical environment provided by the polyelectrolyte polymer phase.

Composites are however often more than the sum of their components, with enhanced properties observed from the synergism between these materials. In this context, encapsulation of a polyelectrolyte core within a silica-based shell results in a particulate material having the desired compartmentalised functionality. Although in some cases the synthesis of such particle architecture has been successful, the resulting particles still suffer from limited real-world applicability due to their inherent mechanical instability, high solubility of the core in polar solvents, and for being chemically inert.

Accordingly, there remains an opportunity to develop polyelectrolyte polymer- silica core shell particles that offer enhanced real-world applicability.

SUMMARY OF THE INVENTION

The present invention provides a core-shell particle having:

a) a cross-linked polyelectrolyte core, and

b) a silica-based shell having covalently bound thereto one or more groups of formula -R-F, wherein R is an organic group and F is a functional moiety.

By the core being a cross-linked polyelectrolyte core, the mechanical stability of the core shell particle is advantageously superior to that of conventional polyelectrolyte-silica core shell particles. Also, the cross-linked polyelectrolyte core is insoluble in polar solvents and can be stored in dry form, greatly enhancing the practical handling and shelf-life of the core-shell particles. The cross-linked polyelectrolyte core also ensures that the mechanical stability of the particle is preserved also for larger core-shell particles relative to conventional ones.

In addition, by the silica-based shell having covalently bound thereto one or more groups of formula -R-F, wherein R is an organic group and F is a functional moiety, the core shell particle of the present invention is chemically and physically active. As a result, the particle advantageously combines chemo-physical targeting and cargo retention capability. Accordingly, the core- shell particles of the invention are inherently suitable for applications that require a specific interaction between the particle and a target substrate.

In some embodiments, the functional moiety F is selected from a hydroxyl group, an amino acid group, an amide group, an amine group, an imide group, a thiol group, a phosphate group, an epoxy group, an alkyl halide group, an isocyanate group, a hydrazide group, a semicarbazide group, an azide group, an ester group, a carboxylic acid group, an aldehyde group, a ketone group, a disulfide group, a xanthate group, a thiocyanate group, or a thiosulfate group.

In some embodiments, the cross-linked polyelectrolyte core comprises an anionic polyelectrolyte, a cationic electrolyte, or a combination thereof. For example, the cross- linked polyelectrolyte core may comprise a polyelectrolyte selected from poly(acrylamide), poly(acrylic acid), poly(allylamine), poly(ethylenimide), poly(styrene sulfonate), poly(N-isopropylacrylamide), poly(diallyldimethylammonium chloride), and a combination thereof.

In addition, the core- shell particle of the invention may comprise additive species, which may be either core additive or shell additive species depending on whether they are provided in the cross-linked polyelectrolyte core or coordinated to the functional moiety, respectively. Depending on the nature of the additive species, they advantageously provide additional functionality to the core-shell particle of the invention.

The present invention also provides a method for preparing a core-shell particle, the method comprising the steps of:

a) providing a cross-linked polyelectrolyte core template,

b) coating the core template with a silica-based shell, and

c) introducing one or more groups of formula -R-F covalently bound to the silica- based shell, wherein R is an organic group and F is a functional moiety.

By providing a cross-linked polyelectrolyte core template, the core template is advantageously larger and more mechanically stable than conventional polyelectrolyte core templates. Also, the resulting core-shell particle has improved mechanical stability over conventional core-shell particles. The cross-linked polyelectrolyte core template may be provided by any means known to the skilled person. In some embodiments, the core template is synthesised via a water- organic solvent emulsion route. This allows for easy control of the reaction conditions and facile tuning of the core template morphology and composition.

The coating of the core template may be achieved by any means known to the skilled person. In an embodiment, the core template is coated by hydrolysis and condensation reactions of alkoxysilanes and functional alkoxy silanes. The use of alkoxysilanes and functional alkoxysilanes to provide a silica-based shell advantageously affords a high degree of chemical customisation of the silica-based shell.

While the silica-based shell may be provided directly on the core template, the present invention also allows for the provision of intermediate layers between the core template and the silica-based shell. For example, the core-shell particle of the invention may include one or more intermediate layers between the core template and the silica-based shell, wherein the one or more intermediate layers are selected from an oppositely charged polyelectrolyte relative to the cross-linked polyelectrolyte core, a two dimensional anionic material such as graphene oxide, silica, calcium carbonate, metal nanoparticles of the kind described herein, a surfactant, or a combination thereof.

The introduction of one or more groups of formula -R-F covalently bound to the silica- based shell may be achieved by any route known to the skilled person.

In some embodiments, the one or more groups of formula -R-F covalently bound to the silica-based shell are introduced by promoting hydrolysis and condensation of functional alkoxysilanes comprising one or more groups of formula -R-F covalently bonded to a tetra-coordinated silicon atom. The functional alkoxysilanes may be used together with alkoxysilanes for the provision of a homogeneous dispersion of functional moieties throughout the silica-based shell, or in a two-step approach in which alkoxysilanes are first condensed on the template core to form an initial silica-based surface, followed by condensation of the functional alkoxysilanes on the initial silica-based surface. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be now described with reference to the following non limiting drawings, in which:

Figure 1 shows an optical micrograph of embodiment poly(acrylamide)-silica core-shell particles dispersed in water,

Figure 2 shows diameter distribution of approximately spherical dried poly(acrylamide) template cores,

Figure 3 shows Zeta-potential profiles of poly(acrylamide) cores, poly(acrylamide)-silica, and poly(acrylamide)/poly(acrylic acid)-silica core-shell particles measured at between pH 2-12 in 10 mmol/F NaCl,

Figure 4 shows a) hardness plots measured by Atomic Force Microscope (AFM) for poly(acrylamide) cores and poly(acrylamide)-silica core-shell particles, showing applied force as a function of indentation depth after contact with force set point at 10 nN, and b) transformation of the hardness plot into F = E · k as per Hertz’s model of soft contact,

Figure 5 shows a) hardness plots measured by AFM for poly(acrylamide)/poly(acrylic acid) cores and poly(acrylamide)/poly(acrylic acid)-silica core-shell particles, showing applied force as a function of indentation depth after contact (force set point at 100 nN), and b) corresponding transformation plots into F = E · k as per Hertz’s model of soft contact,

Figure 6 shows a) hardness plots measured by AFM for poly(allylamine) cores and poly(allylamine)-silica core-shell particles, showing applied force as a function of indentation depth after contact (force set point at 100 nN), and b) corresponding transformation plots into F = E · k as per Hertz’s model of soft contact, Figure 7 shows a) EDX (Energy-dispersive X-Ray) spectrum and b) EDX image measured on poly(acrylamide)-silica core-shell particles in which the silica shell comprises mercapto- functions (Scale bar = 20 pm), and c) Secondary electron SEM (Scanning Electron Microscopy) micrograph of the sample (Scale bar = 50 pm),

Figure 8 shows a) optical micrograph of poly(acrylamide)-silica core-shell particles in which the shell is decorated with Au nanoparticles (Scale bar = 50 pm), b) TEM (Transmission Electron Microscopy) micrograph of a section of the shell showing Au nanoparticles decorating the shell (Scale bar = 100), and c) TEM micrograph of a detail of the shell decorated with Au nanoparticles (Scale bar = 10 nm),

Figure 9 shows a) Benzyl alcohol conversion and selectivity for benzoic acid as a function of reaction time during reaction using poly(acrylamide)-silica core-shell particles having the shell decorated with Au nanoparticles, and b) turnover frequency as a function of time for 12.4 mg/g catalyst, Au : benzyl alcohol = 1 : 800, at 70°C,

Figure 10 shows a) benzaldehyde and benzoic acid yields with repeated reuse of the catalytic material at Au : benzyl alcohol = 1 : 800, at 60°C, 4 hours reaction time, and b) Arrhenius plot for benzyl alcohol oxidation using 12.4 mg/g catalyst, Au : benzyl alcohol = 1 : 800, 4 hours reaction time (lines are for reference only),

Figure 11 shows a) phosphate ion release from 0.020 w/v% poly(allylamine)-silica core shell particle containing 360 mg/g P0 4 3- in water as a function of time, and b) a schematic of adsorption scenarios based on adsorption affinity between dissolved ions and cross- linked polyelectrolyte cores,

Figure 12 shows release plot of phosphate ions as a function of a) time and b) NaCl concentration, at 0.25 w/v% poly(allylamine)-silica (360 mg/g, 8.7X 10 -3 mol/F [P0 4 3- ]), t = 48 hours (lines are for reference only),

Figure 13 shows the magnetic response of dispersed poly(acrylamide)-silica core-shell particles having a core containing magnetite nanoparticles (3.0 mg/g dry) after settling for 10 minutes without (a) and in the presence (b) of an external magnetic field,

Figure 14 shows optical micrographs of the core-shell particles of Figure 13 moving under the influence of an external magnetic field within 6 seconds of applying the field,

Figure 15 shows fluorescent micrographs of core-shell particles surface-functionalised with bovine serum albumin (BSA) tagged with fluorescein isothiocyanate (FITC),

Figure 16 shows mercapto-functionalised silica-PEI core-shell particles deposited (a) on a gold component of an electronic circuit board, and (b) on a pristine gold surface,

Figure 17 shows comparative values of adhesive force between mercapto-functionalised silica-PEI core-shell particles and a silicon substrate (left distribution), and between the same particles and a gold surface (right distribution),

Figure 18 shows effectiveness of gold extraction using mercapto-functionalised silica-PEI core-shell particles adsorbed on gold surfaces as a function of (a) time and (b) concentration of particles,

Figure 19 shows fragments of a printed circuit board component (a) in its pristine form, and (b) after gold extraction from the contact electrodes using mercapto-functionalised silica-PEI core-shell particles,

Figure 20 shows flutriafol release (%) from the alkyl-functionalised core-shell particles into water as a function of time,

Figure 21 shows adsorption of perflurooctanoic acid (PFOA) into the core of silica— PEI core-shell particle adsorbent as a function of PFOA equilibrium concentration, and

Figure 22 shows PFOA concentration in contaminated soil before and after treatment with dilute sodium chloride solution (left) and mixture of dilute sodium chloride solution and silica— PEI core- shell particle adsorbent.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a core-shell particle.

By being a“particle” is meant that the core-shell particle is a discrete subdivision of matter. Generally, the core-shell particle will range in size from fractions of nanometers (nm) to several units of millimetres (mm) as measured in terms of its largest dimension. The particle of the invention is a“core-shell” particle, meaning that the particle comprises an inner core that is either wholly covered or otherwise surrounded by an outer shell layer. As a result of the core being either wholly covered or otherwise surrounded by the outer shell layer, the Young Modulus of the particle increases relative to the Young Modulus of the core absent the shell.

Provided the core-shell particle of the invention has a largest size from fractions of nanometers (nm) to several units of millimetres (mm), there is no particular limitation as to the exact size of the core-shell particle. In some embodiments, the largest dimension of the core-shell particle is between about 1.0 nm to about 5 mm, between about 1.0 nm to about 1 mm, between about 10 nm to about 750 pm, between about 50 nm to about 750 pm, between about 100 nm and 750 pm, between about 100 nm and 500 pm, between about 100 nm and 250 pm, between about 100 nm and 100 pm, between about 250 nm and 100 pm, between about 500 nm and 100 pm, between about 750 nm and 100 pm, between about 1 pm and 100 pm, or between about 1 pm and 50 pm.

In some embodiments, the core-shell particle is spheroidal in shape, such that its dimension can be measured in terms of a largest diameter. In this case the largest diameter of the core-shell particle is between about 1.0 nm to about 5 mm, between about 1.0 nm to about 1 mm, between about 10 nm to about 750 pm, between about 50 nm to about 750 pm, between about 100 nm and 750 pm, between about 100 nm and 500 pm, between about 100 nm and 250 mih, between about 100 nm and 100 mih, between about 250 nm and 100 mih, between about 500 nm and 100 mih, between about 750 nm and 100 mih, between about 1 mih and 100 mih, or between about 1 mih and 50 mih.

In some embodiments, the core-shell particle of the invention is substantially spherical in shape such that its dimension can be measured in terms of a diameter. In this case the diameter of the core-shell particle is between about 1.0 nm to about 5 mm, between about 1.0 nm to about 1 mm, between about 10 nm to about 750 pm, between about 50 nm to about 750 pm, between about 100 nm and 750 pm, between about 100 nm and 500 pm, between about 100 nm and 250 pm, between about 100 nm and 100 pm, between about 250 nm and 100 pm, between about 500 nm and 100 pm, between about 750 nm and 100 pm, between about 1 pm and 100 pm, or between about 1 pm and 50 pm.

The core-shell particle of the invention comprises a cross-linked polyelectrolyte core. As it would be understood by a skilled person, a“polyelectrolyte” means a polymer having at least one ionic side group. Suitable examples of ionic side groups include -sulfonate groups, -ammonium groups, -imidazolium group, -amine groups, -amide groups, -imide groups, -carboxy groups, and -phosphonate groups.

By having a“cross-linked polyelectrolyte core”, the core-shell particle of the invention has a core that is either entirely made of cross-linked polyelectrolyte or a core in which a major component is a cross-linked polyelectrolyte. In some embodiments, the cross-linked polyelectrolyte core comprises from 51% to 100% of polyelectrolyte, from 75% to 100% of polyelectrolyte, from 80% to 100% of polyelectrolyte, from 85% to 100% of poly electrolyte, from 90% to 100% of polyelectrolyte, or from 95% to 100% of polyelectrolyte by weight.

Accordingly, the core may include any one or more components that are chemically compatible with the cross-linked poly electrolyte. For instance, the core may include one or more polymer(s) other than the cross-linked polyelectrolyte. This can be advantageous for modulating the chemical character of the core. For example, the core may include a polymer having one or more hydrophobic moieties, the fraction of which may be tailored to tune the overall hydrophilic/hydrophobic character of the core. In addition, the core may include one or more additives species that confer the particle additional chemical and/or physical properties. For example, the core may include one or more additives species of the kind disclosed herein.

Provided the polyelectrolyte has at least one ionic side group, there is no limitation to the nature of the polyelectrolyte. In some embodiments, the polyelectrolyte is selected from an anionic polyelectrolyte, a cationic polyelectrolyte, or a combination thereof.

For example, the polyelectrolyte may be selected from poly (acrylamide), poly(acrylic acid), poly(allylamine), poly(ethylenimine), poly(styrene sulfonate), poly(N- isopropylacrylamide), poly(diallyldimethylammonium chloride), and a combination thereof.

In some embodiments, the polyelectrolyte is selected from poly(acrylamide), poly(allylamine), poly(acrylic acid), poly(ethylenimine), poly(methacrylic acid), and a combination thereof. Examples of suitable combinations of polyelectrolytes for use in the invention include poly(acrylamide)/poly(acrylic acid), and poly(methacrylic acid)/poly(acrylamide).

In the core-shell particle of the invention the polyelectrolyte is a cross-linked poly electrolyte. By the polyelectrolyte being“cross-linked” is meant that at least two polyelectrolyte chains or at least two locations of a polyelectrolyte chain are covalently connected to one another through a cross-linking agent, resulting in a three-dimensional open-lattice molecular structure. Since the polyelectrolyte is cross-linked, the resulting core-shell particle can be larger in size relative to corresponding core-shell particles in which the polyelectrolyte is not cross-linked, and preserve mechanical robustness despite its larger size. Also, by the polyelectrolyte being cross-linked the core is advantageously insoluble in a polar solvent and can be preserved in dry state. This significantly facilitates its handling and shelf-life for practical purposes. Provided the polyelectrolyte is cross-linked, there is no limitation as to the nature of the cross-linking agent used to achieve the cross-linking. Suitable examples of cross-linking agents include those described herein.

In some embodiments, the cross-linked polyelectrolyte is in the form of a gel. By the term “gel” is meant a cross-linked system that presents as a solid, jelly-like material that, when in steady-state, exhibits no flow and can support its own weight when in steady-state. As would be known to a skilled person, a typical characteristic of a gel is its ability to swell as a result of accumulation of fluid within its volume. Advantageously, the cross-linked polyelectrolyte core can therefore be used as a carrier to entrain species.

The cross-linked polyelectrolyte core may comprise core additive species. Provided the core additive species can be provided in the polyelectrolyte core, there is no limitation to their chemical nature. In some embodiments, the core additive species are selected from nanoparticles, microparticles, ions, bio-molecules, cells, and a combination thereof.

In some embodiments, the cross-linked polyelectrolyte core comprises nanoparticles. By the term“nanoparticle” is meant a discrete subdivision of matter ranging in size from fractions of nanometers (nm) to hundreds of nanometers (nm) as measured in terms of its largest dimension.

In some embodiments, the nanoparticles are magnetic nanoparticles. As used herein, the expression“magnetic nanoparticles” refers to nanoparticles possessing a permanent or induced dipole moment. Examples of magnetic nanoparticles suitable for use in the present invention include those made of a ferromagnetic, a ferromagnetic, an anti-ferromagnetic, a paramagnetic, or a super-paramagnetic material. When the core of the core-shell particle of the invention further comprises magnetic nanoparticles, core-shell particles suspended in a fluid medium can be easily isolated from the fluid medium by the application of an external magnetic field, for example with a magnet. Examples of suitable magnetic nanoparticles include nanoparticles made of a metal material, a magnetic material, a magnetic alloy, or a combination thereof. The metal material may include at least one selected from Pt, Pd, Ag, Cu, and Au. The magnetic material may include at least one selected from Co, Mn, Fe, Ni, Gd, Mo, M3O4, MM 2O4, and M x M y , wherein M and M' are each independently Co, Fe, Ni, Mn, Zn, Gd, or Cr, and 0<x<3 and 0<y<5. The magnetic alloy may include at least one selected from CoCu, CoPt, FePt, CoSm, NiFe, and NiFeCo. In some embodiments, the magnetic particles comprise particles made of at least one metal oxide selected from oxides of iron, oxides of manganese, oxides of cobalt, oxides of zinc, oxides of nickel and oxides of copper. In some embodiments, the magnetic nanoparticles are magnetite (Fe 3 04) nanoparticles.

Provided the magnetic nanoparticles can be provided in the cross-linked polyelectrolyte core, there is no limitation as to their size or shape. In some embodiments, the magnetic particles have a maximum dimension of from about 1 nm to about 500 nm, from about 1 nm to about 100 nm, from about 1 nm to about 50 nm, or from about 1 nm to about 10 nm.

Also, provided the magnetic nanoparticles can be provided in the cross-linked polyelectrolyte core, there is no limitation as to their concentration in the cross-linked polyelectrolyte core. In some embodiments, the concentration of magnetic particles in the core is between about 0.1 wt% and about 15 wt%, between about 0.5 wt% and about 15 wt%, between about 1 wt% and about 15 wt%, between about 1 wt% and about 10 wt%, or between about 1 wt% and about 5 wt%.

In some embodiments, the cross-linked polyelectrolyte core comprises Quantum Dots (“QDs”). By the term“QDs” is meant either (i) semiconductor nanoparticles having a maximum dimension that is smaller than the exciton Bohr radius of the specific semiconductor forming the QDs (herein "semiconductor QDs"), or (ii) carbon nanoparticles comprising amorphous to nanocrystalline cores with predominantly graphitic or turbostratic carbon (sp 2 carbon) or graphene and graphene oxide sheets fused by diamond-like sp 3 hybridised carbon insertions (herein "C-QDs"). In a semiconductor QD the electronic excitation levels of the semiconductor material are confined in three dimensions, resulting in the material having electronic properties between those of the bulk semiconductor and a discrete molecule. As a result, semiconductor QDs shows size-dependent opto-electronic properties.

For example, when excited with an external light source semiconductor QDs emit light at a wavelength which, for a given semiconductor material, is dictated by the size of the semiconductor QDs. Accordingly, when exposed to a suitable external light source a core shell particle of the invention comprising semiconductor QDs would emit light at specific wavelengths depending on the nature of the semiconductor QDs and their size.

In some embodiments, semiconductor QDs are provided in the form of monodisperse nanoparticles. In some embodiments, the semiconductor QDs comprise monodisperse semiconductor QDs having a maximum dimension of between about 1 nm to about 50 nm, between about 1 nm to about 25 nm, between about 1 nm to about 10 nm, between about 1 nm to about 7 nm, or between about 1 nm to about 5 nm. When monodisperse in size, the semiconductor QDs can emit light along a narrow range of wavelengths.

Examples of suitable core-type semiconductor QDs for use in the invention include CdS QDs, CdSe QDs, ZnS QDs, ZnSe QDs, InAs QDs, HgS QDs, ZnTe QDs, PbS QDs, PbSe QDs, CdTe QDs, InP QDs, CuInS QDs, and a combination thereof.

Examples of suitable core-shell semiconductor QDs for use in the invention include (according to a core/shell notation) CdS/ZnS QDs, CdSe/ZnS QDs, CdSe/ZnSe QDs, CdSe/CdS QDs, InAs/CdSe QDs, CdS/HgS QDs, CdS/CdSe QDs, and ZnSe/CdSe QDs, ZnTe/CdSe QDs, CdTe/CdSe QDs, CdS/ZnSe QDs, and a combination thereof.

Examples of suitable alloyed semiconductor QDs for use in the invention include CdSei- x S x QDs, CdSei- x Te x QDs, CdTei- x S y QDs, Cdi- x In x S QDs, and a combination thereof. Alloyed QDs may also be provided as core/shell QDs. For example, the alloyed QDs may be selected from alloyed core-shell semiconductor QDs such as CdSei- x S x /ZnS, CdSei- x Te x /ZnS, Cdi- x In x S/ZnS and a combination thereof.

In some embodiments, C-QDs are provided in the form of monodisperse nanoparticles. In some embodiments, the C-QDs comprise monodisperse C-QDs having a maximum dimension of between about 1 nm to about 50 nm, between about 1 nm to about 25 nm, between about 1 nm to about 10 nm, between about 1 nm to about 7 nm, or between about 1 nm to about 5 nm. Examples of C-QDs and details of their synthesis may be found in Shi Ying Lim, et al., "Carbon quantum dots and their applications” , Chem. Soc. Rev., 2015, 44, 362, the content of which is incorporated herein in its entirety.

Provided the semiconductor QDs or C-QDs can be provided in the cross-linked polyelectrolyte core, there is no limitation as to their amount. In some embodiments, the amount of semiconductor QDs or C-QDs in the cross-linked polyelectrolyte core is between about 0.1 and about 10 wt %, between about 0.1 wt% and about 5 wt%, or between about 0.1 wt% and about 1 wt%.

In some embodiments, the cross-linked polyelectrolyte core comprises microparticles. By the term "microparticles" is meant a discrete subdivision of matter ranging in size from hundreds of nanometers (nm) to hundreds of micrometers (pm) as measured in terms of its largest dimension.

Examples of suitable microparticles include microparticles made of magnetic materials described herein. As long as the magnetic microparticles can be provided in the cross- linked polyelectrolyte core, there is no limitation as to their size or shape. In some embodiments, the magnetic microparticles have a maximum dimension of from about 100 nm to about 500 pm, from about 1 pm to about 100 pm, from about 1 pm to about 50 pm, or from about 1 pm to about 10 pm.

Also, as long as the magnetic microparticles can be provided in the cross-linked polyelectrolyte core, there is no limitation as to their concentration in the cross-linked polyelectrolyte core. In some embodiments, the concentration of magnetic microparticles in the core is between about 0.1 wt% and about 15 wt%, between about 0.5 wt% and about 15 wt%, between about 1 wt% and about 15 wt%, between about 1 wt% and about 10 wt%, or between about 1 wt% and about 5 wt%.

In some embodiments, the cross-linked polyelectrolyte core comprises an ionic species. For avoidance of doubt it will be understood that the“ionic species” of these embodiments is in addition to the at least one ionic side group of the poly electrolyte. The“ionic species” of these embodiments will be understood to be an atom or molecule with a net electric charge due to the loss or gain of one or more electrons.

Provided the ionic species can be provided in the cross-linked polyelectrolyte core, there is no particular limitation to the nature of the ionic species. Examples of suitable ionic species include (i) potassium ions (K + ), (ii) nitrogen-containing ions such as nitrate ions (N0 3 ) and ammonium ions (NH 4 + ), (iii) phosphorous -containing ions such as phosphate ions (P0 4 3 ), hydrogen phosphate ions (HP0 4 2_ ), and dihydrogen phosphate ions (H 2 P0 4 ), (iv) sulfur-containing ions such as sulphate (S0 4 2 ) and thiosulfate (S2O2 2 ), (v) iodide (G), (vi) ions of transition metals belonging to the d-block of the Chemical Periodic Table, examples of which include iron(II,III), copper (I, II), gold(I,III), and silver(I)), (vii) ions of lanthanides belonging to the f-block of the Chemical Periodic Table (i.e. ‘rare-earth metals’) such as ions of neodymium(II,III,IV) and europium(II,III), (viii) ions of alkaline earth metals belonging to the s-block of the Chemical Periodic Table such as ions of calcium(II) and magnesium(II), and (vii) a combination thereof. According to these embodiments the core-shell particle of the invention can advantageously function as slow release fertiliser to promote plant growth since the ionic species can advantageously desorb from the cross-linked polyelectrolyte core to be released into the external environment.

Provided the core- shell particle promotes plant growth, there is no limitation on the amount of nitrogen-containing ions that may be present in the core of the core-shell particle. For example, nitrogen-containing ions may be present in an amount of at least about 15 mg/g, at least about 40 mg/g, at least about 55 mg/g, at least 80 mg/g relative to the weight of the core-shell particle. In some embodiments, nitrogen-containing ions are present in an amount of up to about 350 mg/g, up to about 250 mg/g, or up to 150 mg/g relative to the weight of the core-shell particle. Accordingly, in some embodiments the core of the core-shell particle comprises from about 15 mg/g to about 350 mg/g, from about 40 mg/g to about 250 mg/g, or from about 55 mg/g to 150 mg/g of nitrogen relative to the weight of the core-shell particle.

Provided the core-shell particle promotes plant growth, there also is no limitation on the amount of phosphorous -containing ions that may be present in the core of the core-shell particle of the present invention. For example, phosphorous-containing ions may be present in an amount of at least about 100 mg/g, at least about 150 mg/g, at least about 200 mg/g, or at least about 250 mg/g relative to the weight of the core-shell particle. In some embodiments, the core of the core-shell particle comprises phosphorous-containing ions in an amount of up to about 500 mg/g, up to about 400 mg/g, or up to about 350 mg/g. Accordingly, in some embodiments the core of the core-shell particle comprises from about 50 mg/g to about 500 mg/g, from about 100 mg/g to about 400 mg/g, or from about 150 mg/g to about 350 mg/g of phosphorous-containing ions relative to the weight of the core-shell particle.

Provided the core-shell particle promotes plant growth, there also is no limitation on the amount of potassium ions that may be present in the core of the core- shell particle fertiliser composition of the present invention. For example, potassium may be present in an amount of at least about 10 mg/g, at least about 20 mg/g, at least about 30 mg/g, at least about 40 mg/g. In some embodiments, the core of the core-shell particle comprises potassium in an amount of up to about 250 mg/g, up to about 200 mg/g, or up to about 175 mg/g. Accordingly, in some embodiments the core of the core-shell particle comprises from about 10 mg/g to about 250 mg/g, from about 20 mg/g to about 200 mg/g, from about 30 mg/g to 175 mg/g of potassium relative to the weight of the core-shell particle.

In some embodiments, the cross-linked polyelectrolyte core comprises one or more plant regulator compounds. In some embodiments, the plant regulator compounds are selected from pesticides (such as herbicides, insecticides, and fungicides), plant growth regulators, and a combination thereof. According to these embodiments, the core- shell particle of the invention finds application as agro-chemical regulator for the selective growth inhibition of unwanted plants.

Provide the core- shell particle functions as intended, there is no limitation to the amount of plant regulator compounds. For example, the plant regulator compounds may be present in an amount of between about 0.05 wt% to about 5 wt%, between about 0.12 and about 1.0 wt %, between about 0.12 wt% and about 0.4 wt% relative to the weight of the core-shell particle.

Examples of suitable herbicides include s-triazine type herbicides such as atrazine and 2- chloro-4-ethylamino-6-isopropylamine-s-triazine, sulfonylureas such as trifloxysulfuron, nicosulfuron, metsulfuron, amidosulfuron, sulfosulfuron and triasulfuron; triazines such as simazine and atrazine; dinitroanilines such as prodiamine, pendimethalin and oryzalin; triazolinones such as sulfentrazone, thiencarbazone and carfentrazone; pyridines such as dithiopyr and triclopyr; ureas such as diuron and fenuron; difenyl ethers such as formesafen and oxyfluorofen; chloroacetamides such as acetochlor and s-metolachlor; cyclohexanedione oximes such as clethodim; isoxazoles such as isoxaflutole; triketones such as mesotrione, tembotrione, topramezone, and sulcotrione; bipyridyliums such as diquat and paraquat; glycines such as glyphosate; phosphinic acids such as glufosinate; and benzoic acids such as dicamba.

Example of suitable insecticides include abamectin, cyanoimine, acetamiprid, thiodicarb, nitromethylene, nitenpyram, clothianidin, dinotefuran, fipronil, lufenuron, pyripfoxyfen, thiacloprid, fluxofenime, imidacloprid, thiamethoxam, chloranthraniliprole, beta cyfluthrin, lambda cyhalothrin, fenoxycarb, diafenthiuron, pymetrozine, diazinon, disulphoton, profenofos, furathiocarb, cyromazin, cypermethrin, tau-fluvalinate, tefluthrin, spinosad, etofenprox, carbosulfan, propaphos, permethrin, bensultap, benfuracarb, rynaxypyr and Bacillus thuringiensis products. In some embodiments the pesticides are selected from abamectin, thiodicarb, cyanoimine, acetamiprid, nitromethylene, nitenpyram, clothianidin, dinotefuran, fipronil, thiacloprid, imidacloprid, thiamethoxam, chloranthraniliprole, beta cyfluthrin, lambda cyhalothrin, tefluthrin, and a combination thereof.

Examples of suitable fungicides include azoxystrobin, bitertanol, carboxin, Cu 2 0, cymoxanil, cyproconazole, cyprodinil, dichlofluamid, difenoconazole, diniconazole, epoxiconazole, fenpiclonil, fludioxonil, fluoxastrobin, fluquiconazole, flusilazole, flutriafol, furalaxyl, guazatin, hexaconazole, hymexazol, imazalil, imibenconazole, ipconazole, kresoxim-methyl, mancozeb, metalaxyl, mefenoxam, metconazole, myclobutanil, oxadixyl, pefurazoate, penconazole, pencycuron, prochloraz, propiconazole, pyroquilone, (±)-cis- 1 -(4-chlorophenyl)-2-( 1H- 1 ,2,4-triazol- 1 -yl)cycloheptanol, spiroxamin, tebuconazole, thiabendazole, tolifluamide, triazoxide, triadimefon, triadimenol, trifloxystrobin, triflumizole, triticonazole, uniconazole, isoprothiolone, carpropamid, thifluzamide, tiadinil, probenazole, diclocymet, furametpyr and orysastrobin. Particularly suitable fungicides include azoxystrobin, propiconazole, difenoconazole, fludioxonil, thiabendazole, tebuconazole, metalaxyl, mefenoxam, myclobutanil, fluoxastrobin, tritaxonazole and trifloxystrobin. In particular, there may be mentioned azosystrobin, fludioxonil and mefenoxam.

Examples of suitable plant growth regulators include paclobutrazol and trinexapac-ethyl, and acibenzolar-S-methyl.

In some embodiments, the cross-linked polyelectrolyte core further comprises a bio molecule. As used herein, the term “bio-molecule” and its variants comprise any compound isolated from a living organism, as well as synthetic or recombinant analogs or mimics, derivatives, mutants or variants and/or bioactive fragments of the same. For example, the bio-molecule can be a protein, a peptide, a nucleic acid, a nucleotide, or an amino acid.

As used herein, the term‘bioactive’ and its variants such as‘bioactivity’ used in reference to a bio-molecule refer to any in vivo or in vitro activity that is characteristic of the bio molecule itself, including the interaction of the bio-molecule with one or more targets. For example, bioactivity can include the selective binding of an antibody to an antigen, the enzymatic activity of an enzyme, and the like. Such activity can also include, without limitation, binding, fusion, bond formation, association, approach, catalysis or chemical reaction, optionally with another bio-molecule or with a target molecule.

Provided the cross-linked polyelectrolyte core comprises a bio-molecule, there is no particular limitation regarding the concentration of the bio-molecule in the cross-linked polyelectrolyte core. Suitable concentrations of the bio-molecule in the cross-linked polyelectrolyte core can include a range of between about 0.01 and about 100 mg/g, between about 0.01 and about 75 mg/g, between about 0.1 and about 50 mg/g, between about 0.1 and about 25 mg/g, between about 0.2 and about 25 mg/g, between about 0.25 and about 25 mg/g, between about 0.25 and about 20 mg/g, between about 0.25 and about 15 mg/g, between about 0.25 and about 10 mg/g, and between about 0.025 and about 1.5 mg/g.

In one embodiment, the bio-molecule is an amino acid.

As used herein, the expression‘amino acid’ refers to an organic acid containing both a basic amine group (NH 2 ) and an acidic carboxyl group (COOH). The expression is used in its broadest sense and may refer to an amino acid in its many different chemical forms including a single administration amino acid, its physiologically active salts or esters, its combinations with its various salts, its tautomeric, polymeric and/or isomeric forms, its analogue forms, its derivative forms, and/or its decarboxylation products.

Examples of amino acids useful in the invention comprise, by way of non-limiting example, Agmatine, Beta Alanine, Arginine, Asparagine, Aspartic Acid, Cysteine, Glutamine, Glutamic Acid, Glycine, Histidine, Isoleucine, Leucine, Lysine, Methionine, PhenylBeta Alanine, Proline, Serine, Threonine, Tryptophan, Tyrosine, and Valine.

In one embodiment, the bio-molecule is a protein. As used herein, the term‘protein’ refers to a polymer of amino acid residues and to variants and synthetic analogues of the same. Thus, these terms apply to amino acid polymers in which one or more amino acid residues is a synthetic non-naturally occurring amino acid, such as a chemical analogue of a corresponding naturally occurring amino acid, as well as to naturally-occurring amino acid polymers. As used herein, the term ‘protein’ also embraces an enzyme.

In accordance with the invention, the protein may be selected from therapeutic or prophylactic proteins. These may include plasma proteins, hormones and growth factors, extracellular proteins, and protein antigens for vaccines. They may also be selected from structurally useful proteins for use in cosmetics and foods. Examples of plasma proteins include, but are not limited to Albumin (HSA), haemoglobin, thrombin, fibronectin, fibrinogen, immunoglobulins, coagulation factors (FX, FVIII, FIX)). Examples of extracellular proteins (and in some case these are also described as structural proteins) include, but are not limited to collagen, elastin, keratin, actin, tubulin, myosin, kinesin and dynein. Examples of hormones and growth factors include, but are not limited to insulin, EGF, VEGF, FGF, insulin like growth factor, androgens, and estrogens. Examples of antigen proteins include, but are not limited to ovalbumin (OVA), keyhole limpet hemocyanin and bovine serum albumin (BSA) and immunoglobulins.

Proteins that can be used in the invention include enzymes. As used herein, the term ‘enzyme’ refers to a protein originating from a living cell or artificially synthesised that is capable of producing chemical changes in an organic substance by catalytic action.

Enzymes are industrially useful in many areas such as food, textiles, animal feed, personal care and detergents, bioremediation and catalysis. In these application areas, conservation of conformation and activity, bioavailability and release profile and the adoption of an encapsulation carrier all play some role in their industrial utility. Enzymes are also useful in biomedical devices and sensors, owing to their high selectivity. Examples of enzymes used in the food industry include, but are not limited to pectinases, renin, lignin- modifying enzymes, papain, lipases, amylases, pepsin and trypsin. Examples of enzymes used in the textile industry include, but are not limited to endoglucases, oxidases, amylases, proteases cellulases and xylanases. Examples of enzymes used in the biomedical/sensor industry include, but are not limited to dehydrogenases, lipases, horse radish peroxidase (HRP), urease and RNA or DNA enzymes such as ribonuclease.

In one embodiment, the bio-molecule is a nucleic acid.

As used herein, the expression‘nucleic acid’, synonym of the term‘polynucleotide’, refers to polymeric macromolecules, or large biological molecules, essential for all known forms of life which may include, but are not limited to, DNA (cDNA, cpDNA, gDNA, msDNA, mtDNA), oligonucleotides (double or single stranded), RNA (sense RNAs, antisense RNAs, mRNAs (pre -mRN A/hnRN A) , tRNAs, rRNAs, tmRNA, piRNA, aRNA, RNAi, Y RNA, gRNA, shRNA, stRNA, ta-siRNA, SgRNA, Sutherland RNA, small interfering RNAs (siRNAs), double-stranded RNAs (dsRNA), short hairpin RNAs (shRNAs), piwi- interacting RNAs (PiRNA), micro RNAs (miRNAs), small nucleolar RNAs (SnoRNAs), small nuclear (SnRNAs) ribozymes, aptamers, DNAzymes, ribonuclease-type complexes and other such molecules as herein described. For the avoidance of doubt, the expression 'nucleic acid' includes non-naturally occurring modified forms, as well as naturally occurring forms.

In some embodiments, the nucleic acid molecule comprises from about 8 to about 80 nucleobases (i.e. from about 8 to about 80 consecutively linked nucleic acids). One of ordinary skill in the art will appreciate that the present invention embodies nucleic acid molecules of 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28,

29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76,

77, 78, 79, or 80 nucleobases in length.

In some embodiments, the cross-linked polyelectrolyte core comprises a cell. As used herein, the term‘cell’ means a biological unit comprising a membrane-bound cytoplasm. That is, a cell suitable for use in the invention is a cell provided with all structural features of a living cell, i.e. a whole cell. In that context, such a cell may be, for example, a eukaryotic cell or a prokaryotic cell, including a genetically-modified cell, a cell containing the same genetic material as a naturally-occurring cell, a cell from a line of cells, or one isolated from an organism.

In some embodiments, the cell is a eukaryotic cell. A eukaryotic cell comprises genetic material that is enclosed within a nuclear envelope (also known as nuclear membrane, nucleolemma or karyotheca). Multiple eukaryotic cells can organise into complex structures and are the characteristic cells of animals (including humans), plants, fungi, and Protista. Accordingly, the cell may be a eukaryotic cell selected from an animal cell, a plant cell, a fungi cell, and a Protista cell.

In some embodiments, the cell is a prokaryotic cell. Unlike eukaryotic cells, a prokaryotic cell lacks a nuclear envelope separating genetic material from the cytoplasm. Examples of prokaryotic cells include bacterial cells (i.e. unicellular microorganisms belonging to the Domain Bacteria ), and Archea cells (i.e. unicellular microorganisms belonging to the Domain Archea). Accordingly, the cell may be a prokaryotic cell selected from a bacterial cell, and an Archea cell.

The core-shell particle of the invention comprises a silica-based shell.

By the shell being a“silica-based” is meant that a main component of the shell is silica, i.e. silicon dioxide (Si0 2 ). The silica may be microporous, mesoporous or microporous. By being“microporous” the silica has molecular defects with an average size of less than 2 nm (micropores). These may derive from discontinuities and defects of the silica molecular structure due to a portion of silicon atoms being covalently mono-, di-, or tri- coordinated with an element other than oxygen, for example carbon. By being“mesoporous”, the silica has interconnecting voids and orifices with an average size in the range of 2-50 nm (mesopores). By being "macroporous" the silica has interconnecting voids and orifices with an average size larger than 50 nm (macropores). The role of silica in the hybrid materials is twofold: providing a chemical environment with versatile functionality, and preventing physical degradation of the core template.

The silica-based shell has covalently bound thereto one or more groups of formula -R-F, wherein R is an organic group and F is a functional moiety. By the silica-based shell “having covalently bound thereto” one or more groups of formula -R-F is meant that the organic group R of the one or more groups of formula -R-F is covalently bonded to a silicon atom within the silica molecular structure.

By R being an“organic group” is meant that R includes at least one carbon atom. R may therefore be an alkyl group, an alkenyl group, an aryl group, or a carbocyclyl group.

As used herein, the term“alkyl”, used either alone or in compound words, describes a group composed of at least one carbon and hydrogen atom, and denotes straight chain, branched or cyclic alkyl, for example C1-20 alkyl, e.g. Ci-io or Ci- 6 . Examples of straight chain and branched alkyl include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, t- butyl, n-pentyl, l,2-dimethylpropyl, 1,1 -dimethyl-propyl, hexyl, 4-methylpentyl, 1- methylpentyl, 2-methylpentyl, 3-methylpentyl, l,l-dimethylbutyl, 2,2-dimethylbutyl, 3,3- dimethylbutyl, l,2-dimethylbutyl, l,3-dimethylbutyl, l,2,2-trimethylpropyl, 1,1,2- trimethylpropyl, heptyl, 5-methylhexyl, l-methylhexyl, 2,2-dimethylpentyl, 3,3- dimethylpentyl, 4,4-dimethylpentyl, l,2-dimethylpentyl, l,3-dimethylpentyl, 1, 4-dimethyl pentyl, l,2,3-trimethylbutyl, l,l,2-trimethylbutyl, l,l,3-trimethylbutyl, octyl, 6- methylheptyl, l-methylheptyl, l,l,3,3-tetramethylbutyl, nonyl, 1-, 2-, 3-, 4-, 5-, 6- or 7- methyloctyl, 1-, 2-, 3-, 4- or 5-ethylheptyl, 1-, 2- or 3-propylhexyl, decyl, 1-, 2-, 3-, 4-, 5-, 6-, 7- and 8-methylnonyl, 1-, 2-, 3-, 4-, 5- or 6-ethyloctyl, 1-, 2-, 3- or 4-propylheptyl, undecyl, 1-, 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-methyldecyl, 1-, 2-, 3-, 4-, 5-, 6- or 7-ethylnonyl, 1-, 2-, 3-, 4- or 5-propyloctyl, 1-, 2- or 3-butylheptyl, l-pentylhexyl, dodecyl, 1-, 2-, 3-, 4-, 5-, 6-, 7-, 8-, 9- or lO-methylundecyl, 1-, 2-, 3-, 4-, 5-, 6-, 7- or 8-ethyldecy 1, 1-, 2-, 3-, 4-, 5- or 6-propylnonyl, 1-, 2-, 3- or 4-butyloctyl, l-2-pentylheptyl and the like. Examples of cyclic alkyl include mono- or polycyclic alkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl and the like. Where an alkyl group is referred to generally as‘propyl’, butyl’ etc., it will be understood that this can refer to any of straight, branched and cyclic isomers where appropriate.

In some embodiments, R is a linear alkyl group having from 1 to 20 carbon atoms, such as methyl, ethyl, propyl, butyl, hexyl, heptyl, octyl, and the like.

The term“alkenyl” as used herein denotes groups formed from straight chain, branched or cyclic hydrocarbon residues containing at least one carbon to carbon double bond including ethylenically mono-, di- or polyunsaturated alkyl or cycloalkyl groups as previously defined, for example C2-20 alkenyl (such as C2-10 or C2-6). Examples of alkenyl include vinyl, allyl, l-methylvinyl, butenyl, iso-butenyl, 3-methyl-2-butenyl, l-pentenyl, cyclopentenyl, l-methyl-cyclopentenyl, l-hexenyl, 3-hexenyl, cyclohexenyl, l-heptenyl, 3-heptenyl, l-octenyl, cyclooctenyl, l-nonenyl, 2-nonenyl, 3-nonenyl, l-decenyl, 3- decenyl, l,3-butadienyl, l,4-pentadienyl, l,3-cyclopentadienyl, l,3-hexadienyl, 1,4- hexadienyl, l,3-cyclohexadienyl, l,4-cyclohexadienyl, l,3-cycloheptadienyl, 1,3,5- cycloheptatrienyl and l,3,5,7-cyclooctatetraenyl.

The term“aryl” (or‘carboaryl’) denotes any of single, polynuclear, conjugated and fused residues of aromatic hydrocarbon ring systems (e.g. C 6 -24 or Ce-is). Examples of aryl include phenyl, biphenyl, terphenyl, quaterphenyl, naphthyl, tetrahydronaphthyl, anthracenyl, dihydroanthracenyl, benzanthracenyl, dibenzanthracenyl, phenanthrenyl, fluorenyl, pyrenyl, idenyl, azulenyl, chrysenyl. In some embodiments, the aryl group is selected from phenyl and naphthyl.

The term“carbocyclyl” includes any of non-aromatic monocyclic, polycyclic, fused or conjugated hydrocarbon residues, preferably C3-20 (e.g. C3-10 or C3-8). The rings may be saturated, e.g. cycloalkyl, or may possess one or more double bonds (cycloalkenyl) and/or one or more triple bonds (cycloalkynyl). Suitable examples include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, cyclopentenyl, cyclohexenyl, cyclooctenyl, cyclopentadienyl, cyclohexadienyl, cyclooctatetraenyl, indanyl, decalinyl and indenyl. A carbocyclyl group may be optionally substituted by one or more optional substituents as herein defined. The term ‘carbocyclylene’ is intended to denote the divalent form of carbocyclyl. In some embodiments, the carbocyclyl moieties are 5-6-membered or 9-10 membered ring systems.

By F being a“functional” moiety is meant that F contains at least one element other than carbon and hydrogen. For example, F contains an element selected from oxygen, nitrogen, sulphur, bromine, chlorine, fluorine, phosphorous, boron, and aluminium.

Provided it is a functional moiety, there is no limitation as to the chemical nature of F. In some embodiments, F is selected from a hydroxyl group, an amino acid group, an amide group, an amine group, an imide group, a thiol group, a phosphate group, an epoxy group, an alkyl halide group, an isocyanate group, a hydrazide group, a semicarbazide group, an azide group, an ester group, a carboxylic acid group, an aldehyde group, a ketone group, a disulfide group, a xanthate group, a thiocyanate group, or a thiosulfate group.

When the silica-based shell has covalently bound thereto more than one groups of formula -R-F, those groups may be the same or different.

In some embodiments, the silica-based shell has groups of formula -R-F that are identical to one another. In other embodiments, the silica-based shell has groups of formula -R-F, each of which having R and F independently selected from any one of the respective moieties described herein.

In some embodiments, the core-shell particle of the invention comprises shell additive species coordinated to the functional moiety F. Provided they can coordinate to the functional moiety F, there is no limitation to the nature of the shell additive species.

The shell additive species coordinated to the functional moiety may be nanoparticles. Accordingly, in some embodiments the core-shell particle further comprises nanoparticles coordinated to the functional moiety. Advantageously, by having nanoparticles coordinated to the functional moiety the core- shell particle of the invention acquires the chemical and physical characteristics of the coordinated nanoparticles.

Provided they can coordinate to the functional moiety, there is no limitation to the nature of the nanoparticles. Accordingly, in some embodiments the core- shell particle of the invention further comprises metal nanoparticles coordinated to the functional moiety. Examples of metal nanoparticles include Au nanoparticles, Ag nanoparticles, Cu nanoparticles, Pt nanoparticles, Pd nanoparticles, Ru nanoparticles, Re nanoparticles, and a combination thereof. In some embodiments, the core-shell particle further comprises Au nanoparticles coordinated to the functional moiety. In some embodiments, the nanoparticles are selected from magnetic nanoparticles and QDs as described herein.

An aspect of the present invention also relates to a method for preparing a core- shell particle.

A step of the method requires providing a cross-linked polyelectrolyte core template.

The polyelectrolyte may be synthesised by promoting polymerisation of any suitable polyelectrolyte precursor known to a skilled person. Provided it can be used to synthesise a polyelectrolyte, there is no particular limitation to the chemical nature of the polyelectrolyte precursor. Examples of suitable polyelectrolyte monomer precursors include acrylamide, allylamine hydrochloride, acrylic acid, ethylene imine, 4- styrenesulfonic acid sodium salt, N-isopropylacrylamide, and diallyldimethylammonium chloride.

The provision of a cross-linked polyelectrolyte core template includes a step of cross- linking a polyelectrolyte. Cross-linking of a polyelectrolyte may be achieved by any means known to the skilled person. For example, the polyelectrolyte may be exposed to a cross- linking agent. By the expression“cross-linking agent” is meant a chemical compound that is capable to establish a covalent link between at least two discrete polyelectrolyte chains or at least two locations of a polyelectrolyte chain, resulting in the at least two polyelectrolyte chains or the at least two locations of a polyelectrolyte chain to be covalently bonded through the cross-linking agent. In some embodiments, the cross- linking agent has two or more reactive groups, each of which may be made to react with an ionic side group of a polyelectrolyte.

By cross-linking the polyelectrolyte it is advantageously possible to obtain polyelectrolyte template cores that are larger than conventional polyelectrolyte template cores in which the polyelectrolyte is not cross-linked. Also, the cross-linked polyelectrolyte affords the core superior mechanical stability relative to conventional polyelectrolyte core templates. This results in a number of advantages. For example, cross-linked polyelectrolyte core templates are insoluble in conventional solvents, making them extremely easy to handle either in suspended form (e.g. in a solvent) or in dry state. Also, cross-linked polyelectrolyte cores have significantly longer shelf life relative to conventional poly electrolyte core templates.

Provided the cross-linking agent is effective in cross-linking the polyelectrolyte, there is no particular limitation to the chemical nature of the agent. Examples of suitable cross-linking agents include N,N’-methylenebisacrylamide, epichlorohydrin, bis(2- methacryloyl)oxyethyl disulphide, l,4-bis(4-vinylphenoxy)butane, divinylbenzene, p- divinylbenzene, glycerol ethoxylate, glycerol ethoxylate-co-propoxylate, hexa(ethylene glycol) dithiol, 2-[8-(3-hexyl-2,6-dioctylcyclohexyl)octyl]pyromellitic diimide oligomer, 2-[8-(3-hexyl-2,6-dioctylcyclohexyl)octyl] pyromellitic diimide oligomer, 11- maleimidoundecanoic acid, pentaerythritol ethoxylate, pentaerythritol ethoxylate, pentaerythritol propoxylate, l,4-phenylenediacryloyl, poly(ethylene glycol) bisazide, poly(ethylene glycol) diacrylate 2,4,6,8-tetramethyl-2,4,6,8-tetrakis(propyl glycidyl ether)cyclotetrasiloxane, l,3,5-triallyl-l,3,5-triazine-2,4,6(lh,3h,5h)-trione, triethylene glycol dimethacrylate trimethylolpropane ethoxylate, trimethylolpropane ethoxylate, trimethylolpropane ethoxylate 4-vinylbenzocyclobutene, glutaraldehyde, and a combination thereof.

In some embodiments, the polyelectrolyte template core of the invention is synthesised in a water/organic solvent emulsion system, water being the suspended phase and the organic solvent the continuous phase. A skilled person would be aware of suitable procedures in that regard. In a typical reaction, suitable polyelectrolytes precursors are dispersed in the water phase in the presence of a polymerisation initiator and a cross-linker of the kind described herein.

Provided the polyelectrolyte forms, there is no particular limitation to the amount of polyelectrolytes precursors used in the synthesis. In some embodiments the polyelectrolyte precursor is dispersed in the water phase at precursor-to-water weight ratio of between about 1:100 and about 1: 1.

Provided it initiates polymerisation, there is also no particular limitation to the chemical nature and amount of the polymerisation initiator used in the synthesis. For example, the polymerisation initiator may be selected from ammonium persulphate, azobisisobutyronitrile, potassium persulfate, tetramethylethylenediamine, and a combination thereof. In some embodiments, the polymerisation initiator is used in an initiator-to-polyelectrolyte precursor weight ratio of from about 1:100 to about 1:2.

Provided it cross-links the polyelectrolyte, there is also no particular limitation to the amount of cross-linking agent suitable for use in the method of the invention. In some embodiments, the cross-linking agent-to-polyelectrolyte precursor weight ratio is from about 1:100 to about 1:5.

The method of the present invention also requires the coating of the core template with a silica-based shell. Provided the coating results in a silica-based shell as described herein, there is no particular limitation to how this is achieved.

In some embodiments, the silica-based shell is provided by promoting hydrolysis and condensation reactions of alkoxysilanes and functional alkoxysilanes, which results in hydrolysed alkoxysilanes and hydrolysed functional alkoxysilanes condensing around the template core to form a silica-based shell of the kind described herein. In some embodiments, the alkoxysilanes and the functional alkoxysilanes are pre-hydrolysed (or partially pre-hydrolysed) in a medium separate from the medium containing the core template before are made to condense around the template core.

By the term“alkoxysilane” used in isolation is meant compounds that contain one to four organic groups covalently bonded to a silicon atom through an oxygen atom, as opposed to being covalently bonded directly to the silicon atom. In the context of the present invention the alkoxysilanes may be selected from (1) tetraalkoxysilanes, (2) trialkoxy silanes, (3) dialkoxysilanes, (4) monoalkoxysilanes, (5) trialkoxy silanes, or a combination thereof, respectively represented by the following formulae (1), (2), (3), (4) and (5):

Si(OR 1 ) 4 (1),

R 2 R 3 R 4 Si(OR 1 ) (4), and

(R 1 0) 3 Si— R 5 — S OR 1 ^ (5), wherein each of R 1 , R 2 , R 3 and R 4 independently represents an organic group R of the kind described herein, and R 5 represents a divalent hydrocarbon group having 1 to 20 carbon atoms. In some embodiments, R 1 , R 2 , R 3 , and R 4 are the same organic group.

Example of specific alkoxysilanes compounds of this type include methyltriethoxysilane (MTES), phenyltriethoxysilane (PTES), diethyldiethoxysilane, methyltrimethoxysilane (MTMS), dimethyldimethoxysilane, phenyltrimethoxysilane (PTMS), vinyltrimethoxysilane (VTMS), vinylriethoxysilane (VTES), tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), tetrapropoxysilane (TPOS), tetrabutoxysilane (TBOS), and a combination thereof.

By the expression“functional alkoxysilanes” is meant compounds that contain one to three organic groups covalently bonded to a silicon atom through an oxygen atom, and at least one to three groups of formula -R-F covalently bonded directly to the silicon atom, as appropriate such that the silicon atom is tetra-coordinated. In some embodiments, the functional alkoxysilanes are selected from functional trialkoxy silanes, functional dialkoxysilanes, functional monoalkoxysilanes, and a combination thereof, respectively represented by the following formulae (6)-(ll):

(^OfcSi^-F) (6),

(R 1 0)Si(R 2 )(R 3 )(R 4 F) (9),

(R 1 0)Si(R 2 )(R 3 F)(R 4 F’) (10), and

(R 1 0)Si(R 2 F)(R 3 F’)(R 4 F”) (11). wherein each of R 1 , R 2 , R 3 and R 4 independently represents an R group of the kind described herein, and each of F, F’, and F” is independently selected from a hydroxyl group, an amine group, an amide group, a thiol group, a phosphate group, an epoxy group, an alkyl halide group, an isocyanate group, a hydrazide group, a semicarbazide group, an azide group, an ester group, a carboxylic acid group, an aldehyde group, a ketone group, a disulfide group, a xanthate group, a thiocyanate group, and a thiosulfate group. In some embodiments, R 1 , R 2 , R 3 and R 4 are the same organic group. In some embodiments, F, F’, and F” are the same functional moiety.

Examples of specific functional alkoxysilanes compounds suitable for use in the present invention include 3-aminopropyl triethoxysilane, 3-aminopropyl trimethoxysilane, 3- isocyanatopropyl triethoxysilane, 3-isocyanatopropyl trimethoxysilane, 3-azidopropyl triethoxysilane, 3-azidopropyl trimethoxysilane, 3-thiolpropyl trimethoxysilane (or 3- mercaptopropyl trimethoxysilane or trimethoxysilyl propanethiol), 3-thiolpropyl triethoxysilane (or 3-mercaptopropyl triethoxysilane or triethoxy silyl propanethiol), 3- cyanopropyl trimethoxysilane, 3-cyanopropyl triethoxysilane, N-(2-aminoethyl)-3- aminopropyl trimethoxysilane, N-(2-aminoethyl)-3-aminopropyl triethoxysilane, (aminoethylaminomethyl) phenethyl trimethoxysilane, (3-acetamidopropyl) trimethoxysilane, acetoxyethyl trimethoxysilane, 3-acrylamidopropyl trimethoxysilane, acryloxymethyl trimethoxysilane 3-bromopropyl trimethoxy silane, 3-chloropropyl trimethoxysilane, (heptadecafluoro- 1 , 1 ,2,2-tetrahydrodecyl) trimethoxysilane,

(heptadecafluoro- 1 , 1 ,2,2-tetrahydrodecyl) triethoxysilane, 2-[methoxy(polyethyleneoxy) 2i- 24 propyl] trimethoxysilane, and a combination thereof.

In some embodiments, the silica-based shell is provided by exposing the core template to a mixture of pre-hydrolysed alkoxysilane and a pre-hydrolysed functional alkoxysilane, in which case the step of coating the core template with a silica-based shell is contemporaneous to the step of introducing one or more groups of formula -R-F covalently bound to the silica-based shell.

In other embodiments, pre-hydrolysed alkoxysilanes are first condensed on the core template, and functional alkoxysilanes are subsequently added to the condensed alkoxysilanes. The functional alkoxysilanes can either be pre-hydrolysed before being added to the condensed alkoxysilanes, or hydrolysed in-situ directly on the condensed alkoxysilanes.

Pre-hydrolysis of alkoxysilanes and functional alkoxysilanes can be performed by exposing alkoxysilanes and functional alkoxysilanes, either together or separately, to water in presence of an acid or a base. Details of available pre -hydrolysis procedures are available in David Levy, Marcos Zayat, The Sol-Gel Handbook: Synthesis, Characterization, and Applications , 3 Volume Set, September 2015 (ISBN: 978-3-527- 33486-5), the content of which is incorporated herein in its entirety). In some embodiments, the alkoxysilanes and functional alkoxysilanes are pre-hydrolysed by the addition of and acid, for example hydrochloric acid. Provided the alkoxysilanes and functional alkoxysilanes hydrolyse (either completely or partially), there is no particular limitation to the amount of acid. In some embodiments, each gram of alkoxysilane or functional alkoxysilanes is made to react with from 1 to 250 pl of a 1 M solution of hydrochloric acid.

Provided the silica-based shell with one or more -R-F groups forms on the core template, there is no limitation as to the amount of alkoxysilanes and functional alkoxysilanes used in the method relative to the amount of core template. In some embodiments, the weight ratio of alkoxysilanes to core template is between about 1:1,000 to about 1:1, between about 1:750 to about 1:1, between about 1:500 to about 1:1, between about 1:250 to about 1:1, between about 1:100 to about 1:1, between about 1:75 to about 1:1, between about 1:50 to about 1:1, between about 1:25 to about 1:1, between about 1:10 to about 1:1, between about 1:5 to about 1:1, between about 1:5 to about 1:1, or between about 1:2 to about 1:1. Similarly, the weight ratio of functionalised alkoxysilanes to core template is between about 1:1,000 to about 1:1, between about 1:750 to about 1:1, between about 1:500 to about 1:1, between about 1:250 to about 1:1, between about 1:100 to about 1:1, between about 1:75 to about 1:1, between about 1:50 to about 1:1, between about 1:25 to about 1:1, between about 1:10 to about 1:1, between about 1:5 to about 1:1, between about 1:5 to about 1:1, or between about 1:2 to about 1: 1.

In some embodiments, the method of the invention further comprises coordinating shell additive species to the functional moiety of the silica-core shell.

Provided they can be coordinated to the functional moiety of the silica-core shell, there is no particular limitation to the nature of the shell additive species. In some embodiments, the shell additive species are selected from a nanoparticle, a microparticle, a bio-molecule, and a combination thereof, of the kind described herein. A skilled person would be aware of synthetic procedures that can be adopted to coordinate the shell additive species to the functional moiety of the core-shell particle of the invention. For example, core-shell particles of the invention may be suspended in a solvent having the additive species dispersed therein. Alternatively, the additive species may be added to a suspension of core shell particles of the invention.

Provided it can be coordinated to the functional moiety of the silica-core shell, there is no particular limitation to the amount of the shell additive species relative to the amount of core-shell particles. For example, the weight ratio of additive species to core-shell particles may be about 1:1000 to about 1:20. EXAMPLES

Materials

Acrylamide (98%), N,N’-methylenebisacrylamide (99%), ammonium persulfate (98%), N,N,N’,N’-tctramcthylcthylcncdiaminc (99%), tetraethoxysilane (TEOS, 99%), (3- mercaptopropyl)-trimethoxysilane (MPTMS) (95%), cyclohexane (99%), sorbitan monooleate (70%), poly(allylamine hydrochloride) (PAH, 4.5xl0 5 g/mol, 99%), sodium phosphate (99%), iron (II) chloride tetrahydrate (99%), iron (III) chloride (97%), ammonium molybdate tetrahydrate (83%) and potassium antimony tartrate (99%) were purchased from Sigma Aldrich. Hydrochloric acid (HC1, 32%), sodium hydroxide (NaOH, 99%) and epichlorohydrin (99%) were purchased from Chem- Supply (Australia). Tris(hydroxymethyl)aminomethane hydrochloride (tris-HCl, 99%) was purchased from VWR lifescience. Sodium tetrachloroaurate (III) trihydrate (99%), sodium acetate (98%) and l-ascorbic acid (99.7%) were purchased from BDH Chemicals. Acetic acid (99.7%) and sulfuric acid (98%) were purchased from Ajax Finechem. Trisodium citrate dihydrate (99%), sodium chloride (NaCl, 99.5%), disodium hydrogen phosphate (99%), sodium di hydrogen phosphate (99%), iso-propyl alcohol (99.5%) and ethanol (96%) were purchased from Merck Chemicals. Water was sourced from a Millipore Milli-Q water system (> 18.2 MW-cm). The acrylamide monomer was recrystallised from acetone before use, and all other chemicals were used without further purification.

EXAMPLE 1

Synthesis of core template comprising poly(acrylamide)

Acrylamide was recrystallised from acetone before use. In a typical synthesis acrylamide (1.0 g), N,N’-methylenebisacrylamide (0.04 g) and ammonium persulfate (0.20 g) were dissolved in water (1.67 g). Sorbitan monooleate (0.10 g) was dissolved in cyclohexane (10 mL). The aqueous phase was dispersed into the organic under stirring at 1000 RPM and N,N,N’ ,N’-tetramethyl ethyl enediamine (50 pL) added to the dispersion. The emulsion was left stirring for 4 hours to allow completion of the reaction. EXAMPLE 2

Silica-based shell formation on core templates comprising poly(acrylamide) TEOS (1.0 g) was hydrolysed by the addition of hydrochloric acid (1 mol/L, 20 pL) under stirring for 5 minutes before being left to phase separate. In a typical synthesis, hydrolysed TEOS (0.l-0.5g) was subsequently added to the suspension of poly(acrylamide) core templates and gently stirred for 24 hours to allow deposition to complete. Following this reaction, the hybrid material was centrifuged in cyclohexane (3x), iso-propanol (3x) and ultra-pure water (3x). Samples were either stored as aqueous dispersions under refrigeration or were freeze dried using a Labconco Freezone 2.5, and stored under an inert atmosphere prior to use.

EXAMPLE 3

Synthesis of core-shell particles decorated with Au nanoparticles

Mercapto-functionalised silica was synthesised by the addition of 3-mercaptopropyl trimethoxysilane (MPTMS, 1.0 mL) to a silica-poly(acrylamide) dispersion in ethanol, which was then left gently stirring for 24 hours to allow the reaction to come to completion. The dispersions were centrifuged, redispersed in water (3x) and refrigerated prior to use. Sodium tetrachloroaurate (III) trihydrate (0.0198 g) was dissolved in water (45 mL) and brought to a rolling boil. Trisodium citrate dihydrate solution (1 w/v%, 5 mL) was added to the boiling solution and left for 5 minutes for the reaction to come to completion. The colloidal suspension was cooled on ice. The gold nanoparticle suspension (15-60 mL) was added to the core-shell particles functionalised with mercapto- groups (0.50 g dry basis) in order to produce a gold decorated core-shell particle dispersion, which was refrigerated prior to use. UV-vis spectrophotometry was used to determine the concentration of Au nanoparticles (on a gravimetric basis) in the supernatant both prior to and following gold deposition, allowing quantification of the gold loading on the capsule surface. EXAMPLE 4

Poly(allylamine)-silica core-shell particle synthesis Poly(allylamine hydrochloride)(0.50 g) and NaOH (0.05 g) were dissolved in water (1.0 g). Sorbitan monooleate (0.30 g) was dissolved in cyclohexane (10 mL). The aqueous phase was dispersed in the organic under stirring at 1000 RPM and epichlorohydrin (25 pL) added to the dispersion. The emulsion was left stirring for 4 hours to allow completion of the reaction. The deposition of the silica-based shell was subsequently performed via the method described in Example 2.

EXAMPLE 5

Characterisation methods Nano cale imaging

Samples for scanning electron microscopy (SEM) were freeze dried, dispersed on silicon, and coated in carbon (10 nm) prior to analysis with a dual beam FEI Quanta 3D FEG SEM equipped with an energy-dispersive X-ray spectroscopy (EDX) detector for elemental analysis. Samples for transmission electron microscopy (TEM) were freeze dried, embedded in Struers epofix resin and cured at room temperature for 24 hours. Thin sections (< 60 nm) were cut from the resin via a Reichert Ultracut S ultramicrotome and placed on a copper TEM grid prior to analysis with a FEI Tecnai G2 F20 S-TWIN FEG TEM. Atomic force microscopy (AFM) was undertaken to determine the size of the synthesised AuNPs using a JPK Nanowizard 3 Bioscience AFM. A small quantity (< 20 pL) of the AuNP dispersion was spin coated onto a glass slide prior to analysis. All images were recorded in air using intermittent contact mode with antimony doped silicon cantilevers (model NCHY) from Bruker Corporation. Micro-mechanical characterisation

For the collection of indentation data the dispersion was added to a water-filled petri dish and analysed in liquid. Force data were recorded using silicon nitride cantilevers (model MSCT) from Bruker Corporation, unless otherwise stated. Cantilever spring constants were determined using the Hutter and Bechhoefer method (as described in J. L. Hutter, J. Bechhoefer, Rev. Sci. Instrum. 1993, 64, 1868-1873, the entire content of which is incorporated herein) prior to analysis. Catalytic activity characterisation

The catalytic activity of the gold nanoparticle decorated microcapsule material was investigated by the oxidation of benzyl alcohol. Benzyl alcohol (0.2 mol/L) and sodium hydroxide (0.3 mol/L) were dissolved in a methanol/water (50/50 v/v %) mixture. In a typical reaction, gold-containing capsule suspension (0.25 g) was added to the alkaline alcohol mixture, heated to 60°C and the reaction was left to proceed for 4 hours. At the completion of the reaction, the liquid phase was recovered by centrifugation. In recycling tests, the catalytic material was washed with water (3x) before re-use. The supernatant was analysed via reverse phase high performance liquid chromatography (HPLC) using an Agilent 1220 Infinity II LC (water/acetonitrile 40/60 v/v % solvent, Cis column) to isolate, identify and quantify the reaction products.

Phosphate adsorption within core of core-shell particle A phosphate buffer solution (0.10 mol/L P0 4 3 , 0.10 mol/L NaCl, pH 7.4) was prepared as an adsorbate stock. An acetate buffer solution (0.10 mol/L, pH 5.0), a tris(hydroxymethyl)aminomethane hydrochloride (tris-HCl) buffer solution (0.10 mol/L, pH 8.5) and a NaCl solution (0.10 mol/L) were prepared as diluents. Sample solutions were prepared by the addition of a diluent to the stock solution to provide a phosphate concentration range 10-10,000 mg/L for each diluent system. A freeze dried sample of poly(allylamine)-silica core-shell particles (0.010 g) was added to this solution and shaken vigorously. The mixture was left to equilibrate for 30 minutes before being settled via centrifugation. The supernatant was diluted in water as appropriate and analysed via a colorimetric phosphate assay (as described in E. monitoring, support laboratory, Method 365.3: Phosphorous, All Forms (Colorimetric, Ascorbic Acid, Two Reagent), tech rep., United States Environmental Protection Agency, 1978, the entire content of which is incorporated herein).

To a diluted sample (2 mL), a freshly prepared solution of ammonium molybdate (7.0 mmol/L) and antimony potassium tartrate (0.3 mmol/L) (160 pL) and a solution of sulfuric acid (11 mol/L, 40 pL) were added and the solution shaken. An ascorbic acid solution (340 mmol/L, 80 pL) was added to the solution, which was mixed again and left for 5 minutes for the chromophoric reaction to come to completion before the absorbance at 650 nm was recorded using UV-vis spectrophotometry.

Phosphate release

For phosphate release studies, poly(allylamine)-silica core-shell particles were loaded with phosphate ions by the method described above. Once the adsorbed amount was known, the core-shell particle suspension was settled by centrifugation, the supernatant discarded and the remaining solid freeze dried prior to use. In a typical experiment, silica- poly(allylamine) with a known phosphate concentration (0.01 g) was dispersed in a sodium chloride solution (0.10 mol/L, 4 mL). The dispersion was left to equilibrate for 48 hours before a sample was taken, separated by centrifugation and the phosphate concentration of the supernatant analysed via the colorimetric method described above.

EXAMPLE 6

Core-shell particle characterisation

Optical microscopy

The molecular weight and dispersity are likely to lie in this range or between 1 X 10 6 — 1 X 10 7 g/mol. As the optical micrograph in Figure 1 indicates, the poly(acrylamide)-silica core- shell particle synthesis led to poly-disperse particles. Upon drying, the particles maintain their sphericity and were not seen to collapse. It was possible to disperse the material in a range of solvents, and the particles were observed to swell in aqueous solutions. The dry core templates have a normal size distribution with a mean diameter of 24.9 pm, as shown in Figure 2.

Following silane addition, the optical appearance of the particles was unchanged, and minimal secondary particle growth was observed. After calcination of the poly(acrylamide)-silica core-shell particles at 550°C the capsules appeared smaller than the air-dried particles, but maintained the sphericity of the as-synthesised material. At the temperature employed in calcination, any organic constituent would be volatilised, and so the spherical structures remaining are indicative of the successful synthesis of a core-shell particle.

Zeta potential

Zeta potential measurements were undertaken via micro-electrophoresis to determine the surface chemistry of the synthesised materials. Figure 3 shows Zeta potential plots measured on poly(acrylamide) core templates, poly(acrylamide)-silica core-shell particles, poly(acrylic acid)-silica core-shell particles, and poly(acrylamide)/poly(acrylic acid)-silica core-shell particles.

Poly(acrylamide) core templates are formally uncharged over the pH range investigated (pKa ~ 15), and so the relatively small magnitude of its charge is unsurprising. After the addition of the silica-based shell, the magnitude of the surface charge on the material increases markedly. The relationship between pH and the zeta potential is representative of bulk silica, indicating its likely presence on the core-shell particle. Zeta potential measurements were also taken for the poly(acrylamide)/poly(acrylic acid)-silica core-shell particles, which exhibit zeta potentials reflective of their strongly poly-anionic and poly- cationic cores respectively. It is likely that the thin silica shell deposited is not sufficiently thick to completely mask the high charge of these core materials. Atomic Force Microscopy

In order to explore the morphology of the poly(acrylamide)-silica core-shell particles, intermittent contact mode AFM imaging of the dried material was undertaken. The surface appears covered in micron-sized features of a highly hygroscopic and adhesive nature, but contain no observable nanometre- sc ale structure, as expected of the amorphous polymeric material. The poly(acrylamide)-silica core-shell particles have a surface coating not present on the template, strongly suggesting that the condensation of silica occurs on the core template surface to form a core-shell architecture, in agreement with the results observed following the calcination of the poly(acrylamide)-silica core-shell particles. Core-shell particles with modified core chemistries (e.g. poly(acrylic acid)/poly(acrylamide)-silica core-shell particle, and poly(allylamine)- silica core-shell particle) show similar appearance to the poly(acrylamide) material, indicating universality of the synthetic procedure. The successful deposition of silica onto core templates comprising poly(allylamine) was confirmed via AFM imaging and indentation experiments. AFM revealed few distinct surface features present, and no obvious protrusions. In contrast, after the addition of TEOS the surface results covered with nanometer scale aggregates, indicating the likely deposition of silica, potentially with secondary nucleation at the shell surface. The level of surface roughness may be due to the cationic nature of the core template surface, which may allow the condensation of silica through a base-catalysed pathway as opposed to the anionic pathway expected for silica condensation onto reference flat surfaces of poly(acrylamide) . Micro-Indentation

The role of silica-based shell is twofold: providing a chemical environment with versatile functionality, and preventing physical degradation of the core template. The previous AFM analysis has shown that the presence of silica changes the surface of the materials, but has not elucidated the structural role of the silica. In order to characterise the degree of physical protection provided by the silica-based coating, indentation tests were undertaken using AFM to measure the compliance of capsules following silane addition.

An array of force-displacement curves were made over the surface of a core-shell particle (5x5 pm, 32x32 curves) to provide a measure of the mechanical response across the surface. The stiffness of poly(acrylamide) core template and poly(acrylamide)- silica core shell particles was measured from the indentation response of the capsules, and the Young’s modulus was determined using the Hertz model of contact (as described in H. Hertz, Journal fiir die reine und angewandte Mathematik 1882, 92, 156-171, and J. D. Berry, S. Mettu, R. R. Dagastine, Soft Matter 2017, 13, 1943-1947, the entire contents of which are incorporated herein in their entirety). Individual force curves and plots reported from these data correspond to the force curve with the smallest deviation from the average of that force map (i.e. the“most representative curve”).

As Figure 4(a) indicates, the stiffness of the particles increased following the addition of the silica-based shell to the template core. The indentation depth decreased from approximately 900 nm to 300 nm for a loading set-point of 10 nN. Figure 4(b) displays the indentation data on axes that emphasise a linear relationship between the applied force and the elastic modulus as calculated by the Hertz equation. For a material fitting this model, the Young’s modulus can be obtained from the gradient of a linear function. Examination of the coefficient of determination of these functions indicates a good fit to the Hertz model across the indentation range investigated.

Nano-indentation experiments were also performed on poly(acrylic acid) -silica core- shell particles and poly(acrylamide)/poly(acrylic acid)-silica core-shell particles, with results shown in Figures 5(a,b) and 6(a, b). As those Figures indicate, the stiffness of the samples increases significantly upon the addition of the silica-based shell. The magnitude of the Young’s modulus increases from the core template to the silica coated polymers (3.5x) for poly(acrylamide)/poly(acrylic acid)-silica core-shell particles and 2.6x for poly(acrylic acid)-silica core-shell particles. The values obtained for the samples investigated are reported in Table 1, with the increase in the Young’s modulus of the samples of 3.8X observed following silica deposition indicating a positive role of the silica-based shell in the mechanical response of the samples relative to the core template. This result highlights the potential of the hybrid to introduce soft functional materials such as hydrogels into applications in which they would otherwise be vulnerable to degradation.

Table 1 - Young’s modulus of samples

Despite different cross-linking agents and concentrations, and different underlying chemistries, the similarity of the mechanical response between these materials provides an indication that the deposition of silica onto the polymer template occurs through a common mechanism that may be applied to an array of hydrophilic polymer templates, allowing the creation of a variety of hierarchal composites.

EXAMPLE 7

Characterisation of core-shell particles decorated with Au nanoparticles

The versatility of the silica coating procedure of the invention was explored by provision of mercapto-functions to the poly(acrylamide)-silica core-shell particles. This was achieved by adding 3-mercaptopropyl trimethoxysilane (MPTMS) to a suspension of poly(acrylamide)-silica core-shell particles. EDX characterisation shown in Figure 7(a) indicates the presence of sulfur within the surveyed sample. Spatial EDX mapping (Figure 7(b)) indicates the presence of sulfur on the core-shell particles, and when this result is compared against the carbon spatial pattern (Figure 7(c) it is apparent that they are not co located. That is, the sulfur species are located in the silica-based shell, indicating that the organo-silane deposits on the silica shell rather being incorporated within the core templates. The EDX spectrum (Figure 7a) collected for the particle survey indicated the presence of carbon, nitrogen, oxygen, and sulfur, as expected for this material.

Deposition of a thiol-functionalised alkoxysilane allows the adsorption of gold nanoparticles to the core-shell particle. Gold nanoparticles show particularly interesting optical properties and have potential applications in a number of fields, from medicine to catalysis, primarily due to their localised surface plasmon resonance and energetic crystal faces. Adsorption and catalytic studies were undertaken to examine the potential of the material as a stable, yet chemically versatile support for a highly active, functional surface.

The adsorption of gold nanoparticles onto the mercapto-functionalised shell was monitored by the distinctive red colour of the unaggregated gold nanoparticle suspension. As Figure 8(a) reveals, the nanoparticles were bound specifically to the surface of the core-shell particle without losing their vibrant colour or aggregating. It is clear from the patchy nature of the coverage (seen in the high magnification micrograph, Figure 8(a)), that the gold was bound to the exterior of the core-shell particle, rather than dispersing within the particle bulk, due to the affinity of gold for the mercapto-functionalised surface.

TEM micrographs were recorded of thin sections of the core-shell particles prepared by ultramicrotomy (the nominal thickness of a section was approximately 60 nm). As Figures 8(b, c) indicate, the gold nanoparticles are clearly visible in high concentration on the external layers of the silica-based shell and are not seen to aggregate. The strong partitioning of gold to the thin band in the centre of this image in Figure 8(b) suggests a surface coating which is highly amenable to nanoparticle deposition, with no affinity for the cross-linked polyelectrolyte core (visible as the dark top-right region of the micrograph in Figure 8(b)) exhibited by the nanoparticles.

Figure 8c is a high magnification TEM micrograph of the gold nanoparticle-decorated shell, close examination of which reveals adsorption of particles with a crystalline and faceted structure. Interestingly, it appears that the particles remain on the surface of the shell, and the exposed gold surface may thus retain the characteristics of the deposited gold nanoparticles.

The catalytic activity of the gold nanoparticles decorating the core-shell particle was investigated to determine whether the deposited gold remained accessible. The model catalytic reaction chosen was the oxidation of benzyl alcohol. Figure 9(a) shows the conversion and selectivity of this reaction, indicating that the adsorbed gold indeed retains its chemical activity. For the first 8 hours, the rate of reaction was approximately zero order, and there appeared to be no decrease in the rate of reaction or the activity of the catalyst. When examined after 20 hours however, the reaction rate had slowed dramatically and aggregation of the catalyst supports was observed. In addition, the reaction was initially highly selective for benzaldehyde, however, as it progressed, the concentration of benzoic acid increased dramatically, eventually resulting in the near disappearance of benzaldehyde as a reaction product. It has previously been reported that the acid product is favoured under the basic conditions employed, likely explaining its eventual predominance.

The turnover frequencies reported in Figure 9b decrease dramatically over the course of the reaction, approximately halving during the 20 hour reaction. The reduced turnover frequency, slowing of the reaction and aggregation of the catalyst supports suggests that the catalyst is highly sensitive to the reaction conditions employed, and may be poisoned or deactivated during the reaction.

The role of heat in the reaction kinetics and catalyst deactivation was investigated directly. Figure 10(d) indicates that the reaction is highly sensitive to the temperature employed. The reaction kinetics at low temperature are shown to increase in an exponential fashion, and is well-described by the Arrhenius equation. The activation energy determined between 20-70°C is 47.2 kJ/mol, in good agreement with reported values. As the reaction can be accurately represented using an Arrhenius model through this range it is likely that the catalytic activity of the gold nanoparticles does not vary significantly over this temperature range. At 80°C, decreased conversion (relative to results between 60-70°C) and significant deviation from the Arrhenius model were observed. This behaviour suggests that high temperature strongly reduces the activity of the gold nanoparticles, however it is not clear whether this is due to the leaching or passivation of the gold, or to weakening of the underlying silica-polymer support.

The gold-decorated core-shell particles could be recycled and reused at length if the reaction was kept below 70°C. As Figure 10(c) indicates, the reaction yield was relatively unchanged over the course of the first several cycles. The subsequent decrease in yield was accompanied by physical changes to the core- shell particles. The core- shell particles were observed to aggregate in solution, and the material appeared purple rather than the red colour previously observed. As Figure 10(c) indicates, the benzaldehyde yield remained constant throughout the tests, and the decrease can be entirely attributed to a decreased yield of benzoic acid, the product of the‘over-oxidation’ of the alcohol. The aggregated gold nanoparticle-decorated core-shell particles could be redispersed and reused following the recovery protocol used for all tests.

EXAMPLE 8

Core modification

Epichlorohydrin cross-linked poly(allylamine) is known to be a high capacity, selective adsorbent for phosphate ions. In order to confirm the utility of the poly(allylamine)-silica core-shell particles, the capacity for phosphate ion adsorption was tested across a range of concentrations. As Figure 11(a) indicates, the cross-linked polyelectrolyte core is an effective adsorbent with a maximum adsorption of 373 mg P0 4 3- (check it matches with proposed embodiment ranges) per gram of poly(allylamine)-silica core-shell particles. This corresponds to an adsorption of 0.354 mol/mol poly(allylamine), slightly above the expected charge stoichiometry. However, there is a clear decrease in the capacity of the cross-linked polyelectrolyte core at high loading capacities. Increasing concentrations of strong kosmotropes (such as the phosphate ion) have been shown to decrease the solubility or‘salt out’ charged macromolecules from solution. This‘salting out’ may collapse the polymer, and reduce its effective adsorption capacity, explaining the decreased capacity observed at elevated phosphate concentrations, as per the schematics of Figure 11(b). While this is an intriguing result, there is considerable uncertainty concerning the mechanism of specific ion-ion and ion-surface interactions.

The long-term stability of the complexed phosphate is critical to its application in environmental and agricultural contexts, controlling its potential to remediate contaminated water or run-off, or used as a controlled release fertiliser. Figure 12(c) is a release profile conducted over a period of 90 days for a poly(allylamine)- silica core- shell particle in a large volume of water (0.2 wt% solids). In the first several hours, approximately 10% of the adsorbed phosphate is released. Beyond this initial period, very little release (up to 12% recovery) was observed over the course of the experiment. This result suggests that there are two modes of phosphate binding. The initially released phosphate appears to be loosely bound or becomes entrained within the cross-linked polyelectrolyte core during the adsorption phases of the experiment, and hence rapidly desorbs when dispersed in the dilute ‘release’ reservoir. The more strongly bound phosphate ions do not desorb to a significant degree over the long timescale investigated, suggesting that the material has a high affinity for phosphate ions and will be a highly effective encapsulation agent.

In order to further examine the relationship between the ionic strength and the degree of phosphate binding to the poly(allylamine)- silica core-shell particle, the release performance of the poly(allylamine)-silica core-shell particle containing phosphate ions was tested in sodium chloride solutions of varying concentration. As Figure 12(d) indicates, there is a strong relationship between the amount released after 48 hours and the ionic strength of solution. When the chloride ion concentration significantly exceeds that of phosphate, it appears to be capable of displacing the loaded phosphate despite the high affinity of the phosphate ion for the amine-containing polymer, providing a means by which to recycle the adsorbent material.

EXAMPLE 9

Nanoparticle fixation and magnetic recovery

Superparamagnetic iron oxide (magnetite) nanoparticles (6 nm, nominal) were dispersed within the poly(acrylamide) during synthesis of the poly(acrylamide) cross-linked polyelectrolyte core template, and the core template coated with a silica-based shell as described in Example 2. As Figure 13 indicates, the magnetic nanoparticles appear to be located within the matrix and provided the poly(acrylamide)- silica core- shell particles as a whole with a high degree of response to an applied external magnetic field. The time lapse sequence shown by the optical micrographs of Figure 14 (taken at 0 seconds, 2 seconds, 4 seconds, and 6 seconds) indicates that the core-shell particles are responsive, and that the magnetic nanoparticles appear to be distributed evenly throughout the cross-linked polyelectrolyte core. These results indicate that magnetic separation is a feasible, straightforward method by which to recover the core-shell particles.

EXAMPLE 10

Biomolecule binding

Bovine serum albumin (BSA) is a protein biomolecule widely used in the biological sciences. It can be readily functionalised with the fluorescent molecule fluorescein isothiocyanate (FITC), without compromising the protein structure or function. Use of the BSA-FITC conjugate provides a straightforward method to visualise BSA when dispersed in aqueous solution.

Poly(acrylamide)— silica core- shell particles were prepared in accordance with the procedure described in Examples 1 and 2. Following synthesis and purification, the particles were dispersed in water (10 w/v %). To this dispersion aminopropyl triethoxy silane (APTES, 0.5 v/v % to polymer) was added and left to react overnight. The dispersion was then centrifuged, with the supernatant discarded and redispersed in water (10 mL) three times before use.

Glutaraldehyde solution (50 uL) was added to the particle dispersion and left to react for 5 minutes under gentle stirring. To this dispersion, BSA-FITC solution (1 mg/L, 100 uL) was added and left 5 minutes to react. Upon addition of the BSA-FITC, the dispersion was strongly yellow coloured. The dispersion was then centrifuged, the supernatant discarded, and redispersed in water (10 mF) three times before use.

The successful binding of BSA to the core-shell particle surface was confirmed via widefield fluorescence microscopy. Images were acquired with an Olympus 1X81 inverted fluorescence microscope with a 20x 0.8 NA oil immersion objective on an Andor iXon Ultra EMCCD camera. The laser used for excitation was Toptica Photonics 200 mW blue (488 nm). All images were collected using the Micromanager program with lOOms exposure and a gain of 100. Images were collected using a 525/50 filter and 488/640 dichroic cube. Corresponding images are shown in Figures 15(a) and 15(b). As Figure 15 indicates, following deposition of BSA-FITC to the functionalised particle surface, the particle material exhibited strong fluorescence under laser excitation at 488 nm. This provides confirmation of the successful binding of BSA to the core-shell surface, and indicates the broad potential of this encapsulation technology for binding and targeting of biomaterials.

EXAMPLE 11

Core-shell particles for mining and e-waste

Cors-shell particles loaded with known metal etchants and functionalised with metallophilic moieties can be used for the direct extraction of metals in either mining or e- waste recycling applications. Materials

Poly(ethylenimine) (PEI, 25,000 g/mol, 99 %), tetraethoxysilane (TEOS, 99 %), (3- mercaptopropyl)-trimethoxysilane (MPTMS, 95 %), cyclohexane (99%), sorbitan monooleate (70 %), and sodium thiosulfate pentahydrate (99%) were purchased from Sigma Aldrich. Hydrochloric acid (32 %), sodium hydroxide (NaOH, 99 %) and epichlorohydrin (99 %) were purchased from Chem-Supply (Australia). Iso-propyl alcohol (99.5 %) and ethanol (96 %) were purchased from Merck Chemicals. Water was sourced from a Millipore Milli-Q water system (> 18.2 MW ah).

Poly( ethylenimine ) core synthesis

PEI (0.50 g) and NaOH (0.05 g) were dissolved in water (1.0 g). Sorbitan monooleate (0.30 g) was dissolved in cyclohexane (10 mL). The aqueous phase was dispersed in the organic under stirring at 1000 RPM 25 and epichlorohydrin (25 pL) added to the dispersion to cross-link the polymer. The emulsion was left stirring for 4 hours to allow completion of the reaction.

Formation of mercapto-functionalised silica shell

TEOS (1.0 g) was hydrolysed by the addition of hydrochloric acid (1 mol/L, 20 pL) under stirring for 5 minutes before being left to phase separate. In a typical synthesis, hydrolysed TEOS (0.1-0.5 g) was subsequently added to the PEI core suspension as described above and gently stirred for 24 hours to allow deposition to complete. Following this reaction, the hybrid material was centrifuged, redispersed and washed in cyclohexane (3x), iso-propanol (3x) and ethanol (3x). Mercapto-functionalised silica-based shell was synthesised by the addition of MPTMS (1.0 mL) to a silica-PEI dispersion in ethanol, which was then left gently stirring for 24 hours to allow the reaction to come to completion. The dispersions were centrifuged, redispersed in water (3x) and refrigerated prior to use. Thiosulfate adsorption

A thiosulfate solution (50 g/L S2O3) was prepared as an adsorbate stock. Sample solutions were prepared by dilution with ultrapure water to provide standard solutions (10-10 000 mg/L, 1 mL). The PEI-functionalised silica core-shell particles (0.20 g) were added as adsorbent to each solution, which were then shaken vigorously. The mixture was left to equilibrate for 30 minutes before being settled via centrifugation. The supernatant was diluted in water as appropriate and the residual sulfur concentration was determined via inductively coupled plasma - optical emission spectroscopy (ICP-OES) using a Perkin - Elmer Avio 200 ICP-OES.

Nanoscale imaging

Samples for scanning electron microscopy (SEM) were freeze dried, dispersed on silicon, and coated with iridium (2 nm thickness, nominal) prior to analysis 40 with a dual beam FEI Quanta 3D FEG SEM equipped with an energy-dispersive X-ray spectroscopy (EDX) detector for elemental analysis.

Micro-mechanical characterisation

For the collection of AFM adhesion data the dispersion was added to a water-filled petri dish and analysed in liquid. Force data were recorded using silicon nitride cantilevers (model NCHV) from Bruker Corporation, unless otherwise stated. Cantilever spring constants were determined using the Hutter and Bechhoefer method prior to analysis (as described in J. L. Hutter, J. Bechhoefer, Rev. Sci. Instrum. 1993, 64, 1868-1873, the entire content of which is incorporated herein). Soft colloidal probes were constructed using dried mercapto-functionalised core-shell particles, synthesised in line with the procedure described above. A small quantity of two-part epoxy resin (Araldite, Bunnings Warehouse) was placed on an AFM cantilever (Bruker NCHV), onto which a single dry particles was deposited and left for 24 hours to cure before use. Metal dissolution experiments

Extraction experiments were undertaken on three gold-bearing substrates, specifically (i) pure gold bullion (Perth Mint, 99.99 %), (ii) a low grade gold ore (pyrite-type, Hellier mine, Australia, 3g/tonne nominal) and (iii) a scavenged printed electronic circuit board. In a typical experiment, the gold-baring substrate (10 g) was dispersed in ultrapure water (100 mL), to which ammonium hydroxide (10 mL) and copper sulfate pentahydrate (0.025 g) were added. Thiosulfate-loaded core-shell particles (5 g) were then added to the mixture and vigorously shaken to disperse. The mixture was then sprayed directly onto the gold- baring substrate using compressed air and left to react for two hours. At the completion of the experiment, the particles were separated from the spent substrate, the gold was eluted from the particles and diluted appropriately for analysis via inductively coupled plasma - mass spectrometry (ICP-MS) using a Perkin-Elmer NexION 350 ICP-MS. Results

Core-shell particles functionalised with mere ap to -functional groups showed strong, specific binding to gold surfaces. Figure 16(a) shows an optical micrograph of a printed circuit board component, which contains a region of gold surrounded by a non-metallic region. The micrograph allows appreciating that the gold-containing region is nearly entirely saturated by the capsules, while coverage on the rest of the surface (darker area surrounding the shaped contact) is low and patchy.

Figure 16(b) shows an optical micrograph of the core-shell particles functionalised with mercapto-functional groups adsorbed on a flat pristine gold surface. The image allows appreciating the affinity of the functionalised capsules for gold surfaces, showing a near monolayer of particles adhering to the surface. Soft colloidal probe studies were subsequently undertaken using atomic force microscopy for direct measurement of the strength of the adhesion between gold surfaces and the functionalised capsules. Figure 17 shows histogram values of the adhesion measured between a single core-shell particle adsorbed onto a gold and a silicon substrate, with significantly greater adhesion observed in the case of the adsorption on gold.

Extraction studies showed that the ensemble system was capable of extracting gold rapidly from each substrate, and under ambient conditions for pure gold, gold bound within e- waste and even low grade gold ore samples. Figure 18 shows data for gold extraction as a function of time (Figure 18(a)) and concentration of core-shell particles (Figure 18(b)).

Figure 19 shows images of (a) a pristine fragment of an electronic circuit board showing gold contact electrodes, and (b) another fragment of the same board after gold extraction using mercapto-functionalised core-shell particles prepared as described in this example.

EXAMPLE 12

Fungicide encapsulation in functionalised core-shell particles

Microcapsule use in agricultural contexts has the potential to challenge existing formulations for controlled spatial and temporal delivery of high-value or toxic agro chemicals. Simple modification of the polymer core of the core-shell particles of the invention to include a hydrophobic polymer group allowed encapsulation of the triazole- type fungicide flutriafol, which showed strong partitioning to the particle and slow release into an aqueous reservoir. In addition, it was shown that with appropriate surface functionalisation, capsules could be made to adhere to plant leaf surfaces specifically, allowing targeted and slow foliar delivery of agro-chemicals.

Poly(methacrylic acid)/poly(acrylamide) core microgel synthesis

In a typical synthesis acrylamide (1.0 g), methacrylic acid (1.0 g), N,N’- methylenebisacrylamide (0.10 g) and ammonium persulfate (0.60 g) were dissolved in water (3.0 g). Sorbitan monooleate (0.10 g) was dissolved in cyclohexane (10 mF). The aqueous phase was dispersed into the organic phase under stirring at 1000 RPM and heated to 70°C. The emulsion was left stirring for 4 hours to allow completion of the reaction. Formation of silica-based shell

TEOS (1.0 g) was hydrolysed by the addition of hydrochloric acid (1 mol/L, 20 pL) under stirring for 5 minutes before being left to phase separate. In a typical synthesis, hydrolysed TEOS (0.1-0.5 g) was subsequently added to the PEI suspension as described above and gently stirred for 24 hours to allow deposition to complete. Following this reaction, the hybrid material was centrifuged, redispersed and washed in cyclohexane (3x), iso-propanol (3x) and ethanol (3x).

Organo-functionalised silica was synthesised by the addition of dimethyldichloro silane (DMDCS) (1.0 mL) to a silica-polymer dispersion in ethanol, which was then left gently stirring for 24 hours to allow the reaction to come to completion. The dispersions were centrifuged, redispersed in water (3x) and refrigerated prior to use.

Cuticle adhesion studies

Adhesion between the alkyl-functionalised capsules and leaf substrates was first measured directly by the deposition of a waxy leaf into an aqueous dispersion of the alkyl- functionalised capsules. After gently stirring of the mixture to ensure adequate diffusion of the capsules the leaf was washed under a high-pressure water stream for 30 seconds and under a nitrogen stream until dry. Following this, the leaf was examined via optical microscopy to determine the degree of surface coverage. In a parallel study, cuticle wax was stripped from leaves (10 g) by immersion in chloroform (100 mL), to produce a wax-containing chloroform solution. Wax coated glass slides were produced by spin coating this solution (60 sec, 5000 RPM, 100 pL) onto a clean glass slide. The glass slide was immersed in the alkyl-functionalised particle dispersion, before washing with a high-pressure water stream for 30 seconds and dried under nitrogen. The transparent, waxy substrate was then examined via optical microscopy to determine the extent of coverage. Aqueous agro-chemical adsorption

A flutriafol dispersion (20 g/L, 10 mL) was prepared as an adsorbate stock. The silica— polymer adsorbent (3.0 g) was added to the mixture and shaken vigorously. The mixture was left to equilibrate for 30 minutes before being settled via centrifugation. The supernatant was taken and the flutriafol concentration determined via high performance liquid chromatography (HPLC). Release studies were undertaken by redispersing the flutriafol- saturated silica— polymer material in ultrapure water (1.0 L) and periodically sampling the mixture.

Optical characterisation (not shown) demonstrate high affinity of the alkyl-functionalised core-shell particles to adhere to the waxy leaf and model substrates, with a large proportion of the material still in place following aggressive treatment of the surfaces. Such treatments were designed to mimic a real use case, in which rainfall and high winds may affect capsule performance. The functionalisation proved to be effective in foliar chemical delivery.

Figure 20 shows flutriafol release (%) from the alkyl-functionalised core-shell particles into water as a function of time. The delayed release observed from the capsule indicates the strong partitioning of the fungicide within the polymer core, highlighting the capability of the material for slow, sustained release of agro-chemicals.

EXAMPLE 13

Perfluro alkyl substance (PFAS) adsorption

For this Example, an organic contaminant (Perfluro alkyl substance, PFAS) is absorbed into the core of core-shell particles. Specifically, pristine particles have been percolated through a PFAS contaminated medium (soil, biomass, et cetera), absorbing the contaminant as they travel, concentrating it within the particle for effective recovery and disposal, and allowing the use of the contaminated medium. Materials

Poly(ethylenimine) (PEI, 25 000 g/mol, 99 %), tetraethoxysilane (TEOS, 99 %), (3- mercaptopropyl)-trimethoxysilane (MPTMS, 95 %), cyclohexane (99%), sorbitan monooleate (70 %), and sodium thiosulfate pentahydrate (99%) were purchased from Sigma Aldrich. Hydrochloric acid (32 %), sodium hydroxide (NaOH, 99 %) and epichlorohydrin (99 %) were purchased from Chem-Supply (Australia). Iso-propyl alcohol (99.5 %) and ethanol (96 %) were purchased from Merck Chemicals. Water was sourced from a Millipore Milli-Q water system (> 18.2 MW-crn).

Poly( ethylenimine ) microgel synthesis

PEI (0.50 g) and NaOH (0.05 g) were dissolved in water (1.0 g). Sorbitan monooleate (0.30 g) was dissolved in cyclohexane (10 mL). The aqueous phase was dispersed in the organic under stirring at 1000 RPM 25 and epichlorohydrin (25 pL) added to the dispersion to cross-link the polymer. The emulsion was left stirring for 4 hours to allow completion of the reaction.

Silica shell deposition

TEOS (1.0 g) was hydrolysed by the addition of hydrochloric acid (1 mol/L, 20 pL) under stirring for 5 minutes before being left to phase separate. In a typical synthesis, hydrolysed TEOS (0.1-0.5 g) was subsequently added to the PEI suspension as described above and gently stirred for 24 hours to allow deposition to complete. Following this reaction, the hybrid material was centrifuged, redispersed and washed in cyclohexane (3x), iso-propanol (3x) and ethanol (3x).

Aqueous flurocarbon adsorption A perflurooctanoic acid solution (PFOA, 10 mL, 200 mg/L) was prepared as an adsorbate stock. Sample solutions were prepared by dilution with ultrapure water to provide standard solutions (10-200 mg/L, 1 mL). The silica— PEI adsorbent (0.01 g) was added to each solution and shaken vigorously. The mixture was left to equilibrate for 30 minutes before being settled via centrifugation. The supernatant was taken and the PFOA concentration determined via liquid chromatography - mass spectrometry (LC-MS).

Flurocarbon adsorption from soil

A perflurooctanoic acid solution (10 mg/L, 200 mL) was added to a soil sample (Bayside, Melbourne AUS, 200g) and vigorously shaken to disperse. The mixture was dried under vacuum for 48 hours to produce a PFOA-contaminated soil (10 mg/kg). Silica— PEI core- shell particles (0.1 g) were dispersed in a dilute sodium chloride solution (0.01 mol/L, 100 mL) to which a sample of PFOA-contaminated soil (50 g) was added. The mixture was shaken vigorously and left to equilibrate for 48 hours. The mixture was settled via centrifugation and the supernatant was taken for analysis via LC-MS.

The synthesised particles show a strong affinity for PFOA, as indicated in Figure 21. While the maximal adsorption capacity was not determined, the sorption behaviour observed indicates the initial core design has a suitably high affinity for PFOA. Through manipulation of the hydrophilic properties of the core, it should be possible to improve this affinity further.

Adsorption of PFOA from a real soil substrate was successfully demonstrated. In Figure 22 removal of PFOA to the instrument detection limit was observed following the addition of a particle suspension to the contaminated soil matrix. This indicates the utility of the core shell particles in a real-use case, showing significant reduction in PFOA concentration in a single pass for highly contaminated soil.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word‘comprise’, and variations such as‘comprises’ and‘comprising’, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.