Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
METHODS OF PRODUCING CONCENTRATED FERROFLUIDS FOR BIOASSAY
Document Type and Number:
WIPO Patent Application WO/2019/103741
Kind Code:
A1
Abstract:
Embodiments of the present disclosure are directed to methods of forming a concentrated ferrofluid, and methods of using the concentrated ferrofluid. In some embodiments, these methods include filtering a ferrofluid comprising a plurality of magnetic nanoparticles, a surfactant and a continuous phase, where the ferrofluidic comprises a first density. The ferrofluidic is dried, where the magnetic nanoparticles and the surfactant remain, and where at least a portion of the continuous phase is removed. A slurry may be formed comprising the dried ferrofluid and the additional amount of the continuous phase. A colloidal suspension comprising a second density of the ferrofluid can be formed by ball milling.

Inventors:
HIRE, Chetan (21 Business Park Drive, Branford, Connecticut, 06405, US)
VOYTA, John C. (21 Business Park Drive, Branford, Connecticut, 06405, US)
Application Number:
US2017/063072
Publication Date:
May 31, 2019
Filing Date:
November 22, 2017
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
ANCERA, LLC (15 Commercial Street, Branford, Connecticut, 06405, US)
HIRE, Chetan (21 Business Park Drive, Branford, Connecticut, 06405, US)
VOYTA, John C. (21 Business Park Drive, Branford, Connecticut, 06405, US)
International Classes:
H01F1/44; B03C1/00; B03C1/005; B03C1/02; H01F1/00
Foreign References:
US6103107A2000-08-15
US5667716A1997-09-16
US20100301257A12010-12-02
US20160299132A12016-10-13
Attorney, Agent or Firm:
HOPKINS, Brian P. et al. (Cooley LLP, Attn.: IP Docketing Department1299 Pennsylvania Avenue NW,Suite 70, Washington District of Columbia, 20004, US)
Download PDF:
Claims:
What is currently claimed is:

1. A ferrofluid concentrating method for concentrating a ferrofluid material, comprising: filtering a ferrofluid, wherein:

the ferrofluid comprises a plurality of magnetic nanoparticles, a surfactant, and a continuous phase, and

the ferrofluid includes a first density;

drying the ferrofluid, wherein at least a portion of the continuous phase is removed; and mixing the at least partially dried ferrofluid with an amount of the continuous phase to form a ferrofluid slurry, wherein the ferrofluid slurry comprises a second density.

2. The method of claim 1, further comprising centrifuging at least one of the ferrofluid and the ferrofluid slurry.

3. The method of claim 1, wherein filtering comprises centrifuging the ferrofluid.

4. The method of claim 1, wherein the second density is greater than the first density.

5. The method of claim 1, wherein drying the ferrofluid comprises removing substantially all of the continuous phase.

6. The method of claim 1, further comprising forming a colloidal suspension by ball milling the ferrofluid slurry.

7. The method of claim 1, wherein the first density comprises between about 1.01 g/cm3 to about 1.40 g/cm3.

8. The method of claim 1, wherein the second density is greater than about 1.01 g/cm3 and up to about 1.80 g/cm3.

9. The method of claim 1, wherein drying comprises at least one of:

freeze drying the ferrofluid, wherein substantially all of the continuous phase is removed; and

spray drying the ferrofluid, wherein substantially all of the continuous phase is removed.

10. The method of claim 1, wherein the continuous phase comprises water.

11. The method of claim 6, wherein forming the colloidal suspension comprises:

forming a ferrofluid comprising a viscosity of between about l.05cP to about 7.0cP; or forming a ferrofluid comprising a pH of between about 8.0 to about 8.5, and a susceptibility of between about 0.26 to about 0.32.

12. The method of claim 1, wherein the amount of the continuous phase is less than about half the amount of the dried ferrofluid.

13. A ferrofluid concentration method for concentrating a ferrofluid material, comprising: providing a ferrofluid, wherein:

the ferrofluid comprises a plurality of magnetic nanoparticles, a surfactant and a continuous phase, and

the ferrofluid includes a first density;

removing at least a portion of the continuous phase from the ferrofluid to form at least a partially dried ferrofluid; and mixing the at least partially dried ferrofluid with an amount of the continuous phase such that a ferrofluid slurry is formed, wherein the ferrofluid slurry is of a second density.

14. The method of claim 13, further comprising centrifuging at least one of the ferrofluid and the ferrofluid slurry.

15. The method of claim 13, wherein filtering comprises centrifuging the ferrofluid.

16. The method of claim 13, wherein the second density is greater than the first density.

17. The method of claim 13, further comprising filtering the ferrofluid prior to removing a portion of the continuous phase.

18. The method of claim 13, wherein removing at least a portion of the continuous phase comprises removing substantially all of the continuous phase, and wherein mixing the substantially dry dried ferrofluid comprises ball milling the dried ferrofluid material.

19. The method of claim 13, wherein the plurality of magnetic nanoparticles comprises a plurality of iron oxide nanoparticles.

20. The method of claim 13, wherein the first density comprises between about 1.01 g/cm3 to about 1.40 g/cm3.

21. The method of claim 13, wherein the second density is greater than about 1.01 g/cm3 to about 1.80 g/cm3.

22. The method of claim 13, wherein drying the ferrofluid comprises freeze drying the ferrofluid.

23. The method of claim 13, wherein drying the ferrofluid comprises spray drying the ferrofluid.

24. The method of claim 13, further comprising forming a colloidal suspension by ball milling the ferrofluid slurry, wherein the colloidal suspension comprises the second density.

25. A ferrofluid composition comprising a plurality of magnetic nanoparticles, a surfactant, and a solvent, wherein a density of the magnetic nanoparticles comprises between about 1.10 g/cm3 and about 1.80 g/cm3.

26. The composition of claim 25, wherein:

the viscosity is between about 1.05 cP and about 7.0 cP;

the pH is between about 7.0 and about 9;

the peak susceptibility comprises between about 0.15 to about 0.50;

the material is capable of being freeze dried and stored at a preferred temperature for up to about one year; and/or

the solvent comprises water.

27. A separation system for separating at least one target from a sample suspended in a ferrofluid, the system comprising:

a concentrated ferrofluid including a sample containing at least one target particle, wherein the ferrofluid comprises a density of between about 1.2 g/cm3 and about 1.8 g/cm3; a microfluidic channel having an inlet, and at least one outlet, wherein the inlet is configured to receive the ferrofluid;

a plurality of electrodes traversing at least a portion of the microfluidic channel length and generating a magnetic field pattern along the microfluidic channel length when a current is applied to at least one of the plurality of electrodes; and wherein the magnetic field pattern is configured to separate the at least one target as the at least one target flows along at least a portion of the microfluidic channel length.

28. The system of claim 27, wherein: the ferrofluid comprises a susceptibility of between about 0.15 to about 0.50;

a ratio of concentrated ferrofluid to the sample comprises between about 1 : 1 to about 1 :5; the sample includes living cells;

the at least one target is separated from the sample based on one or more characteristics of the at least one target;

the at least one target is separated from the sample by directing the at least one target to a selected outlet or trapping the at least one target based on a spacing of at least two electrodes of the plurality of electrodes;

and/or

the at least one target is separated from the sample based on a characteristic of the at least one target selected from the group consisting of target size, target shape, and target elasticity.

29. A ferrofluid concentration method for forming a concentrated ferrofluid, comprising: providing a ferrofluid comprising a plurality of magnetic nanoparticles, a surfactant and a continuous phase, wherein the ferrofluid includes a first density; and removing at least a portion of the continuous phase from the ferrofluid to at least partially dry the ferrofluid to form a ferrofluid slurry including a second density.

30. The method of claim 29, further comprising centrifuging at least one of the ferrofluid and the ferrofluid slurry.

31. The method of claim 29, wherein the second density is greater than the first density.

32. The method of claim 29, wherein removing comprises at least one of:

evaporating a portion of the continuous phase of the ferrofluid, and

using a pressurized filtering process to remove a portion of the continuous phase of the ferrofluid;

utilizing polyethylene glycol to absorb a portion of the continuous phase of the ferrofluid.

Description:
METHODS OF PRODUCING CONCENTRATED FERROFLUIDS FOR BIOASSAY

Field

[0001] The disclosure generally relates to methods of producing concentrated ferro-fluids for bioassay and methods for using same.

Background

[0002] Conventional fluidic devices make use of physical phenomena that apply controlled forces on a stationary collection or stream of particles, molecules, cells or microbeads, to manipulate them in the context of a given assay. Examples of such approaches include microfluidic devices that utilize dielectrophoresis or acoustophoresis for cell separation and capture, as well as immuno- magnetic separation devices that use functionalized magnetic microbeads and externally applied magnetic fields to enrich cell populations. Biocompatible ferrofluids have been used for the controlled manipulation and rapid separation of both microparticles and live cells, where differences in particle size, shape, and elasticity may be utilized to achieve rapid and efficient separation.

SUMMARY OF SOME OF THE EMBODIMENTS OF THE DISCLOSURE

[0003] In some embodiments of the disclosure, a ferrofluid concentrating method for concentrating a ferrofluid material is provided and includes filtering a ferrofluid, where:

- the ferrofluid comprises a plurality of magnetic nanoparticles, a surfactant, and a continuous phase, and

- the ferrofluid includes a first density. The method also includes drying the ferrofluid, where at least a portion of the continuous phase is removed, and mixing the at least partially dried ferrofluid with an amount of the continuous phase to form a ferrofluid slurry, and the ferrofluid slurry comprises a second density.

[0004] Such embodiments may further include one and/or another (i.e., a plurality) of the following additional features, functionality or clarifications (as the case may be), yielding yet further embodiments:

centrifuging at least one of the ferrofluid and the ferrofluid slurry;

filtering comprises centrifuging the ferrofluid;

- the second density is greater than the first density;

drying the ferrofluid comprises removing substantially all of the continuous phase;

forming a colloidal suspension by ball milling the ferrofluid slurry;

- the first density comprises between about 1.01 g/cm 3 to about 1.40 g/ cm 3 ;

- the second density is greater than about 1.01 g/ cm 3 and up to about 1.80 g/ cm 3 ;

drying comprises at least one of:

freeze drying the ferrofluid, where substantially all of the continuous phase is removed; and

spray drying the ferrofluid, where substantially all of the continuous phase is removed.

- the continuous phase comprises water;

forming the colloidal suspension comprises:

forming a ferrofluid comprising a viscosity of between about 1 05cP to about 7.0cP; or

forming a ferrofluid comprising a pH of between about 8.0 to about 8.5, and a susceptibility of between about 0.26 to about 0.32.

and - the amount of the continuous phase is less than about half the amount of the dried ferrofluid.

[0005] In some embodiments of the present disclosure, a ferrofluid concentration method for concentrating a ferrofluid material is provided and includes providing a ferrofluid, where:

- the ferrofluid comprises a plurality of magnetic nanoparticles, a surfactant and a continuous phase, and

- the ferrofluid includes a first density.

The method also includes removing at least a portion of the continuous phase from the ferrofluid to form at least a partially dried ferrofluid, and mixing the at least partially dried ferrofluid with an amount of the continuous phase such that a ferrofluid slurry is formed, wherein the ferrofluid slurry is of a second density.

[0006] Such embodiments may further include one and/or another (i.e., a plurality) of the following additional features, functionality or clarifications (as the case may be), yielding yet further embodiments:

centrifuging at least one of the ferrofluid and the ferrofluid slurry;

filtering comprises centrifuging the ferrofluid;

- the second density is greater than the first density;

filtering the ferrofluid prior to removing a portion of the continuous phase;

removing at least a portion of the continuous phase comprises removing substantially all of the continuous phase, and mixing the substantially dry dried ferrofluid comprises ball milling the dried ferrofluid material;

- the plurality of magnetic nanoparticles comprises a plurality of iron oxide nanoparticles;

- the first density comprises between about 1.01 g/cm 3 to about 1.40 g/ cm 3 ;

- the second density is greater than about 1.01 g/ cm 3 to about 1.80 g/ cm 3 ;

drying the ferrofluid comprises freeze drying the ferrofluid, which may comprise spray drying the ferrofluid;

and forming a colloidal suspension by ball milling the ferrofluid slurry, wherein the colloidal suspension comprises the second density.

[0007] In some embodiments, a ferrofluid composition is provided and comprises a plurality of magnetic nanoparticles, a surfactant, and a solvent, wherein a density of the magnetic nanoparticles comprises between about 1.10 g/cm 3 and about 1.80 g/ cm 3 .

[0008] Such embodiments may further include one and/or another (i.e., a plurality) of the following additional features, functionality or clarifications (as the case may be), yielding yet further embodiments:

- the viscosity is between about 1.05 cP and about 7.0 cP;

- the pH is between about 7.0 and about 9;

- the peak susceptibility comprises between about 0.15 to about 0.50;

- the material is capable of being freeze dried and stored at a preferred temperature for up to about one year;

And

- the solvent comprises water.

[0009] In some embodiments, a separation system for separating at least one target from a sample suspended in a ferrofluid is provided and includes a concentrated ferrofluid including a sample containing at least one target particle, where the ferrofluid comprises a density of between about 1.2 g/cm 3 and about 1.8 g/c m 3 , a microfluidic channel having an inlet, and at least one outlet, wherein the inlet is configured to receive the ferrofluid, a plurality of electrodes traversing at least a portion of the microfluidic channel length and generating a magnetic field pattern along the microfluidic channel length when a current is applied to at least one of the plurality of electrodes, and the magnetic field pattern is configured to separate the at least one target as the at least one target flows along at least a portion of the microfluidic channel length.

[0010] Such embodiments may further include one and/or another (i.e., a plurality) of the following additional features, functionality or clarifications (as the case may be), yielding yet further embodiments:

- the ferrofluid comprises a susceptibility of between about 0.15 to about 0.50; a ratio of concentrated ferrofluid to the sample comprises between about 1 : 1 to about 1 :5;

- the sample includes living cells;

- the at least one target is separated from the sample based on one or more characteristics of the at least one target;

- the at least one target is separated from the sample by directing the at least one target to a selected outlet or trapping the at least one target based on a spacing of at least two electrodes of the plurality of electrodes;

and

the at least one target is separated from the sample based on a characteristic of the at least one target selected from the group consisting of target size, target shape, and target elasticity.

[0011] In some embodiments, a ferrofluid concentration method for forming a concentrated ferrofluid is provided and includes providing a ferrofluid comprising a plurality of magnetic nanoparticles, a surfactant and a continuous phase, wherein the ferrofluid includes a first density; and removing at least a portion of the continuous phase from the ferrofluid to at least partially dry the ferrofluid to form a ferrofluid slurry including a second density.

[0012] Such embodiments may further include one and/or another (i.e., a plurality) of the following additional features, functionality or clarifications (as the case may be), yielding yet further embodiments:

centrifuging at least one of the ferrofluid and the ferrofluid slurry;

- the second density is greater than the first density;

removing comprises at least one of:

evaporating a portion of the continuous phase of the ferrofluid, and using a pressurized filtering process to remove a portion of the continuous phase of the ferrofluid;

and

utilizing polyethylene glycol to absorb a portion of the continuous phase of the ferrofluid. [0013] At least some of the embodiments of the present disclosure, as well as objects, and advantages thereof will be even clearer with reference to the drawings, a brief description of which is provided below, and detailed description, which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] These and other embodiments of the disclosure will be discussed with reference to the following exemplary and non-limiting illustrations, in which like elements are numbered similarly, and where:

[0015] Fig. 1A is a flow chart of a method of preparing a concentrated ferrofluid according to some embodiments of the disclosure;

[0016] FIG. 1B is a flow chart of another method of preparing a concentrated ferrofluid according to some embodiments of the disclosure;

[0017] Fig. 2A represents a schematic illustration of a microfluidic device and particle manipulation platform that may be used in conjunction with the concentrated ferrofluid according to some embodiments of the disclosure;

[0018] Figs. 2B-2D depict graphs of magnetic properties according to embodiments of the disclosure;

[0019] Figs. 3A-3C are graphs characterizing a biocompatible ferrofluid according to some embodiments of the disclosure; and

[0020] Fig. 4 is a simplified schematic of a fluidic network/system according to some embodiments of the disclosure.

DETAILED DESCRIPTION

[0021] Embodiments herein include methods of using and producing a concentrated ferrofluid that can be used in a microfluidic system. The ferrofluid can be concentrated from commercially available ferrofluids or ferrofluids synthesized by published methods to a desired concentration range for particular assay requirements. A higher ratio of sample, such as a bioassay sample, to ferrofluid, is achievable as compared with the commercially prepared ferrofluids. The disclosed methods provide ferrofluids concentrated to desired densities without adversely affecting critical physical properties such as ratio of surfactant to Fe30 4 nanoparticles (for example), magnetic susceptibility, and pH. Also, improved stability of the ferrofluidic material and long-term storage states are achieved. The properties of the ferrofluids described below are measured by diluting the ferrofluid to the concentration specified for intended use. This applies to magnetic susceptibility, pH, viscosity and osmolality. Most commonly, for embodiments described below, the as-received ferrofluid is diluted in phosphate buffered saline (PBS) in the ratio of 1 : 1 (for example). For a concentrated ferrofluid, this dilution ratio with PBS may be 1 :3 (for example).

[0022] FIG. la depicts a flow chart of a method/process 100 of forming a concentrated ferrofluid, according to some embodiments. The concentrated ferrofluid of these embodiments may be utilized for bioassay in such applications as controlled manipulation and rapid separation of both microparticles and live cells, for example. In an embodiment, a commercially manufactured/prepared ferrofluidic material, such as Ferrotec EMG700, for example, may be provided. The commercially prepared, non-concentrated ferrofluid may comprise densities of between about 1.01 g/cm 3 to 1.40 gm/cm 3 . In an embodiment, the commercially prepared ferrofluid may comprise a first concentration, and may comprise a surfactant, magnetic nanoparticles, such as ferroparticles, and a continuous phase, such as water, and/or any other suitable solvent. At step 102 of the method/process 100, the commercially prepared, unconcentrated ferrofluid may be centrifuged. The centrifuge step 102 may serve to remove large particles and/or aggregates from the commercially prepared ferrofluid. In an exemplary embodiment, the ferrofluid comprising the first concentration may be placed in three polypropylene culture tubes, where 50 ml may be placed in each tube, and may be centrifuged at lOOOrcf for about 30 mins, in an embodiment. Any suitable centrifuging equipment and processing parameters may be used, according to the particular application.

[0023] In an embodiment, subsequent to the centrifugation, the commercial/unconcentrated ferrofluid material may be filtered (step 104) to remove large particles and/or aggregated nanoparticles not removed by centrifugation. For example, in an exemplary embodiment, l50ml of Ferrotec EMG700 ferrofluid may be filtered by using a 0.45mih syringe filter into 50 ml polypropylene culture tubes. The filtering process may remove higher sized particles within the ferrofluid, where the particles may comprise iron oxide (Fe30 4 ) nanoparticles. In an exemplary embodiment, the commercial ferrofluid may be transferred into a container, subsequent to the filtering step. For example, the unconcentrated/commercial ferrofluid may be transferred into five 50 ml tubes (where 30ml may be placed into each tube, for example). In some embodiments, filtering comprises centrifugation. The step(s) of filtering and/or centrifugation can be performed one or more times.

[0024] In the next step of process 100 (step 106), substantially all of a continuous phase of the commercial ferrofluid may be removed (most, and in some embodiments, all). The continuous phase may be removed by drying the ferrofluidic material, as in some embodiments, where the magnetic nanoparticles and surfactant remain. In an exemplary embodiment, an amount of the unconcentrated ferrofluid may be placed in a tube, or in a plurality of tubes, (which may comprise polypropylene or any other type of suitable tube), and the unconcentrated ferrofluid may be shell frozen in the tube (e.g., by repeatedly dipping the tube in liquid nitrogen for about thirty seconds and rotating the tube on its side for about two minutes). The opening of the tube containing the shell frozen ferrofluid may then be wrapped in a double layered Kimwipe and the Kimwipe may be secured with a rubber band. The tube(s) containing the frozen ferrofluid may then be placed in a freeze-dryer chamber (having a temperature of -60 degrees Celsius, for example). The ferrofluid may be freeze dried overnight, and may then be removed from the freeze-dryer (i.e., the tubes are removed). In cases where the tubes are cold to the touch, they may be freeze dried for an additional four hours (for example), or longer (i.e., until the tubes are not cold to the touch).

[0025] In another exemplary embodiment, the commercial ferrofluid may be dried to remove substantially all (most, and in some embodiments, nearly all or all) of the continuous phase, using a spray drying technique. For example, in such embodiments, the atomized (fine droplets) of the ferrofluid may be mixed with hot air in a drying chamber to produce highly dispersed dried ferrofluid powder. The atomization/spray drying process may be chosen based on the resulting particle size, particle size distribution and ease of subsequent re-dispersing into the continuous phase. The temperature of drying medium may be adjusted so that at the end of the spray drying process, the ferrofluid particles are not moist or over-dried. At the end of the spray drying process, the particles may be separated from the drying medium using cyclone, bag filters, precipitators and/or scrubbers. [0026] In the next step of process 100, step 108, the completely dry ferrofluid material may be mixed with a specific additional amount of continuous phase (e.g., added to a specific amount of the dried ferrofluid material) to obtain a ferrofluid slurry. The amounts chosen are selected based upon a resulting, desired density of the ferrofluid. In an exemplary embodiment, the ferrofluid slurry may be formed from the freeze dried commercial ferrofluid, where a desired/targeted concentration/density of ferrofluid is prepared of a second concentration that is different than the initial concentration/density of the commercial ferrofluid. In an embodiment, the second density may comprise, for example:

- between about 1.3 g/cm 3 to about 1.4 g/cm 3 ,

- between about 1.3 g/cm 3 to about 1.5 g/cm 3 ,

- between about 1.3 g/cm 3 to about 1.6 g/cm 3 ,

- between about 1.4 g/cm 3 to about 1.5 g/cm 3 ,

- between about 1.4 g/cm 3 to about 1.6 g/cm 3 , and

- between about 1.5 g/cm 3 to about 1.6 g/cm 3 .

The second concentration may vary according to the particular application (i.e., a desired resulting second density). Alternatively, one may go back to the original or lower density based on the particular application. In an embodiment, a mixing process, such as a ball milling process, for example, may be utilized to achieve a uniform colloidal suspension at the desired concentration of the ferrofluid (step 110). In an embodiment, ball mill jars and balls may be prepared, by utilizing a preparation process. In an embodiment, the preparation process may comprise weighing out a desired amount of the freeze dried ferrofluid, such as between about 60gm to about 80 gm, in an embodiment, in a weigh boat, and transferring into a ball mill jar.

[0027] A desired amount of stainless steel balls (9.5mm diameter, for example) may be added to the ball mill jar, and may comprise between about 30 to about 80 in number. In an embodiment, a ratio of the freeze dried ferrofluid to steel balls may comprise about 2: 1, but may be varied, according to a desired density/concentration of the ferrofluid slurry. Approximately 30 to about 50 ml of deionized water (or any other suitable continuous phase) may be added into the jar using a serological pipette, for example. A lid may be placed on the jar, and the jar may be placed into the ball mill. The lid may be placed/fastened to the jar by using a lock nut. In other embodiments, the additional amount of the continuous phase may be about less than about half an amount of the dried ferrofluid material, but the additional amount may be varied according to the particular application.

[0028] In an exemplary embodiment, a ball mill cycle may comprise 400rpm speed, l20mins total time, 5 minute intervals with direction reversal. The ball mill may be started, and after the ball mill cycle is finished, the ball mill jar may be cooled to room temperature. The ball jar may then be opened, and the balls may be separated into two 50ml tubes using a big spatula, for example, while leaving the concentrated ferrofluid in the jar. The concentrated ferrofluid may be placed into 50ml polypropylene culture tubes (about 40ml in each), for example, using a plastic spatula, for example, to scrape the ferrofluid from the walls and the bottom of the ball mill jar. The tubes containing the concentrated ferrofluid may be attached to a rotator and may be rotated overnight. The tubes may then be removed from the rotator, and allowed to stand for about a period of time (e.g., a half an hour, according to some embodiments).

[0029] In another exemplary embodiment, the uniform colloidal suspension of the concentrated ferrofluid slurry may be centrifuged (e.g., 3000 rpm for about two minutes), and the concentrated ferrofluid may then be aliquoted into micro-centrifuge tubes (e.g., l .5ml), and then optionally stored at a predetermine temperature (e.g., 4°C). The centrifuge process serves to remove bubbles from the colloidal suspension. The methods of such embodiments herein result in the manufacture of concentrated ferrofluids to predetermined concentrations without disrupting the desirable physical properties of the ferrofluid material. The ferrofluid material generated, when mixed with a biological sample containing particles or cells, allows the use of a higher sample volume than permitted with an original commercial ferrofluid. The concentrated ferrofluid material generated by the processes described herein also exhibit improved stability. For example, an intermediate product in the process (i.e., dried ferrofluid material) may be stored in a preferred state. For example, a dry lyophilized (freeze dried) ferrofluid may comprise a preferred storage state, and a spray dried ferrofluid may comprise a preferred storage state as well.

[0030] FIG. lb depicts a flow chart of a method 120 of forming a concentrated ferrofluid, which may be utilized for a bioassay of both microparticles and live cells, for example. In an embodiment, a commercially manufactured/prepared ferrofluidic material, such as Ferrotec EMG700, for example, may be provided (step 122). The commercially prepared, non-concentrated ferrofluid may comprise densities of between about 1.01 g/cm 3 and 1.40 gm/cm 3 , for example. In an embodiment, the commercially prepared ferrofluid may comprise a first concentration, and may comprise a surfactant, magnetic nanoparticles, such as ferroparticles, and a continuous phase, such as water, and/or any other suitable solvent.

[0031] At step 124, a partial amount of the continuous phase may be removed from the commercial ferrofluid, where another portion of the continuous phase may remain. In an embodiment, the provided ferrofluid may undergo an accelerated evaporation process to remove a portion of the continuous phase. For example, 60mL of ferrofluid may be weighed in a polypropylene weighing boat (5” by 5”, for example). Based on the percentage solid content of the ferrofluid, an amount of water/continuous phase in the ferrofluid may be calculated. A target weight of the concentrated ferrofluid to be produced may be calculated by subtracting the weight of half the amount of water in the unconcentrated ferrofluid from the total weight of the unconcentrated ferrofluid.

[0032] The weighing boat with ferrofluid may then be placed under a fan (e.g., approx. 6-7 inches away), blowing air at a predetermined flowrate (e.g., 2.5CFM). The ferrofluid may be stirred with a polypropylene spatula for the duration of accelerated evaporation. Periodically, every 30 minutes (for example), the weighing boat with ferrofluid may be removed from under the fan to weigh the ferrofluid. As the weight becomes closer to the target weight of the concentrated ferrofluid, the weight check may be performed more frequently. Once the target weight is reached, the ferrofluid may be transferred to a centrifuge vial and placed on rotator for overnight. The concentrated ferrofluid may comprise a second concentration which is higher in solid content than the first concentration of the commercially provided ferrofluid.

[0033] In another exemplary embodiment, a partial amount of the continuous phase of the commercial ferrofluid may be removed (step 124) utilizing a process of separation by mixing with polyethylene glycol, and/or by a centrifuge process. For example, 5mL of ferrofluid may be mixed with 500mg of polyethylene glycol, which absorbs water from the ferrofluid, in a weighing boat. As mixing is continued, water and polyethylene glycol solution phase separate from the ferrofluid. The water and polyethylene glycol solution may then be removed by decanting while holding the nanoparticles in the weighing boat. Alternatively, centrifuging can also be used to remove a portion of the continuous phase, such as water, and polyethylene glycol solution. The molecular weight and amount of polyethylene glycol and mixing time can be varied to achieve different degrees of continuous phase removal.

[0034] In another exemplary embodiment, a partial amount of the continuous phase of the commercial ferrofluid may be removed utilizing a process of pressurized ultrafiltration (step 124). A target weight of the concentrated ferrofluid to be produced may be calculated by subtracting the weight of half the amount of water in the unconcentrated ferrofluid from the total weight of the unconcentrated ferrofluid. As the weight becomes closer to the target weight of the concentrated ferrofluid, a weight check may be performed more frequently. Once the target weight is reached, the ferrofluid may be transferred to a centrifuge vial and placed on rotator for overnight. The concentrated ferrofluid may comprise a second concentration which is higher in solid content than the first concentration of the commercially provided ferrofluid.

[0035] FIG. 2A illustrates a ferro-microfluidic device 200 (and particle manipulation platform) which can receive a bioassay sample, and where the ferro/microfluidic device 200 is capable of receiving the concentrated ferrofluid of the embodiments herein, such as those prepared according to the embodiments of FIG. 1, in inlet port 206. The microfluid device 200 may further comprise an outlet port 210. FIG. 2A is a top view/perspective schematic of the device/system 200 displaying a microfluidic channel 207 and the underlying electrodes 212 (not drawn to scale). Two output channels from an amplifier provide sinusoidal currents (I.sub. l and I.sub.2) phase-locked 90. degrees with respect to each other.

[0036] The neighboring electrodes on the substrate may be connected in a manner to carry sinusoidal currents in quadrature and support a traveling wave magnetic field within the microfluidic channel. The magnetic field gradient generated may push nonmagnetic microspheres or cells within the microfluidic channel up and into a gap between electrodes 212; the traveling field also causes the cells of a sample to rotate and roll along the channel 207 ceiling, resulting in continuous translation along the length of the channel 207 at frequencies above a threshold. The resulting microparticle motion may be observed with an upright microscope 216 from above and captured with a CCD camera at 18 frames per second, in an embodiment, for further analysis.

[0037] FIG. 2B depicts a graph of a COMSOL simulation of a magnetic field 218 (dark arrows) and magnitude of magnetic flux density 220 across a section of the ferromicrofluidic device at a given instant in time. The device 200 is able to create both magnetic field gradients, resulting in a time-average force on the cells or particles, and local rotation of ferrofluid magnetization, which eventually results in torque on the nonmagnetic particles. Fainter arrows depict the field at every 30. degree within one period. Simulation is for 12-A peak-to-peak current input at 1,670 Hz.

[0038] FIG. 2C is a graph of computed magnetic force 222 and magnetic torque 224 on a 6 micron diameter microsphere along the length 226 of the microchannel with 7- A peak-to-peak input excitation at 4.6 kHz. When the current is turned on, the cells or particles within the sample are pushed away from the electrodes to the top of the channel, due at least in part to magnetic force, where they start to rotate and roll along its length, due at least in part to magnetic torque. The device behavior can thus mimic the frequency-dependent susceptibility of the particular ferrofluid used. For a given particle size, its speed may depend on the local force 216 and torque 218 values along the channel length. FIG. 2D is a graph of computed magnetic force 222 and torque 224 as a function of frequency 221 for the same particle located between electrodes on the channel ceiling. Input current amplitude is 7 A peak to peak; assumed slip factor for all simulations depicted here is 1. For example, at low frequencies, the force dominates, pushing the nonmagnetic microparticles up to the channel ceiling and into the space between the electrodes. In another example, at high frequencies, the rolling microparticles can overcome the diminishing repulsion caused by magnetic force and move continuously along the channel, as illustrated in FIG. 2D.

[0027] Ferrofluids described herein may comprise colloidal mixtures of nanometer sized magnetic particles covered by a surfactant, suspended in a carrier medium that is compatible with the surfactant material. For example, a sample reaction that results in magnetite particles is as follows: 2FeCl3+FeCl2+8NH3+4H 2 0 - » Fe30 4 +8NH 4 Cl

The magnetization of each single-domain particle responds to a high magnetic field with a time constant on the order of 10 mu.s (according to some embodiments). High magnetic field gradients can be used to position the ferrofluid, "Spikes" and other interesting features may appear at the ferrofluid surface in the presence of such high fields.

[0028] In one embodiment, particle diameters can range from about 1 nm to about 100 nm, and any whole or partial increments therebetween. For example, and without limitation, the particle diameters can range between 1-10 nm, 1-20 nm, 5-50 nm, or 10-100 nm. In a preferred embodiment, particle diameters average about 10 nm. Volume fractions may range from 0.1% to about 10%, and any whole or partial increments therebetween. [0029] In another embodiment, the ferrofluids may be biocompatible, such that, live cells exhibit no deleterious effects for several hours in terms of physical properties, allowing for extended examination of the target sample. The biocompatible ferrofluid can be suitable for use with any living cell type and/or shape, such as any animal or plant tissue cell type, any microorganism, or any combination thereof, for example. Of course, the ferrofluid is also suitable for suspending any type of particle, and for any sized or shaped particle, or particle clusters or clumps, whether living or non-living.

[0030] FIGS. 3A-3C, depict graphs characterizing an example of a biocompatible ferrofluid according to some embodiments. FIG. 3A is a graph depicting the distribution of magnetic nanoparticle sizes within a ferrofluid, as obtained by TEM, according to some embodiments. Mean nanoparticle core diameter is about 11.3 +/- 4.4 nm (Scale bar: 50 nm), in some embodiments. In one embodiment, the ferrofluid comprises nanoparticles suspended in water and is stabilized with citrate. From simultaneous fits to ac susceptibility and dc magnetization data (FIG. 3B), the average hydrodynamic diameter was determined to be about 72.5 nm, according to some embodiments. The discrepancy between the average hydrodynamic diameter and the individual core sizes observed in TEM images points to a certain degree of particle aggregation within the colloidal suspension of the ferrofluid. This finding was also confirmed through dynamic light scattering measurements, which yielded an average hydrodynamic diameter of about 64.9 nm on highly diluted samples of ferrofluid. Nevertheless, the magnetic nanoparticles were still of a size which approximate the ferrofluid as a continuous magnetic medium. FIG. 3C is a chart depicting live cell count vs. pH stabilizer concentration. As shown herein, according to some embodiments, 40 mM citrate concentration (titrated with citric acid to a pH of 7.4) is found to be optimum for cell viability and ferrofluid stability combined.

[0031] Fig. 4 depicts a continuous flow device/system 400, which may comprise a microfluidic system, in some embodiments, that is capable of being used to assay various biological samples. The system 400 is capable of separating at least one target from the sample that may be suspended in a ferrofluid, for example. In an embodiment, a sample 404 to be assayed may be suspended within a concentrated ferrofluid within a reservoir 402. The sample 404 (including ferrofluid, cells and or beads, such as microbeads. For example) may enter a device/channel inlet 406, and may be assisted by means of a pump and or pressure source 405. The sample 404 may pass/flow 408 in a direction through a channel/series of channels 407, and may exit via a channel outlet 408. The exiting sample may be directed towards waste or back to the reservoir 402.

[0032] A series of planar electrodes, electromagnets, and or a permanent magnetic array 412 may enable target moieties (such as salmonella cells, etc.) within the sample 404, to be captured at receptor regions 414. For example, the continuous flow device/system may be designed for capturing particles at receptor regions 414 of a particular size. An optional scanner/sensor 416 (which may include electromagnets) may be optionally employed to sense/quantify the amount of captured targeted moieties within a capture/receptor region 414. In an embodiment, a plurality of electrodes 412 may traverse at least a portion of a microfluidic channel 407 length and may generate a magnetic field pattern along the microfluidic channel length 407 when a current is applied to at least one of the plurality of electrodes. In another embodiment, a magnetic field pattern may be configured to separate at least one target moiety as the target flows along at least a portion of the microfluidic channel length. The system depicted in FIG. 4 is thus suitable for sorting two or more particle types based on one or a combination of size, shape and elasticity.

[0033] Other commercially available ferrofluids can be processed by the described methods, such as Ferrotec EMG 304, EMG 308, EMG 408, EMG 507, EMG 508, EMG 509, EMG 605, EMG 607, EMG 700, EMG 705, EMG 707, EMG 708, EMG 805 and EMG 807, as well as DKS1 S9, DKS1 S12, WHKS1 S9-A, WHKS1 S9-B and WHKS1 S9-C from Liquid Research.

[0034] The following embodiments illustrate exemplary and non-limiting embodiments of the disclosure.

[0035] Example 1 includes a method of concentrating a ferrofluid material, which includes filtering a ferrofluid, where the ferrofluid comprises a plurality of magnetic nanoparticles, a surfactant, and a continuous phase, and where the ferrofluid comprises a first density. The method also includes drying the ferrofluid, where at least a portion of the continuous phase is removed, then mixing the at least partially dried ferrofluid with an additional amount of continuous phase to form a ferrofluid slurry. The ferrofluid slurry comprises a second density. In some embodiments, the second density is different from the first density (e.g., a density larger than the first density). Optionally, the ferrofluid (or ferrofluid slurry) may be centrifuged (in some examples, filtering comprises centrifuging). [0036] Example 2 includes the method of example 1, where drying the ferrofluid comprises removing substantially all of the continuous phase.

[0037] Example 3 includes the method of example 1, further comprising forming a colloidal suspension by ball milling the ferrofluid slurry.

[0038] Example 4 includes the method of example 1, where the plurality of magnetic nanoparticles comprises a plurality of iron oxide nanoparticles.

[0039] Example 5 includes the method of example 1, where the first density comprises between about 1 g/cm3 to about 1.6 g/cm3.

[0040] Example 6 includes the method of example 1, where the second density comprises between about 1 g/cm3 to about 1.8 g/cm3.

[0041] Example 7 includes the method of example 1, where drying the ferrofluid comprises freeze drying the ferrofluid, and substantially all of the continuous phase is removed.

[0042] Example 8 includes the method of example 1 , where drying the ferrofluid comprises spray drying the ferrofluid, and substantially all of the continuous phase is removed.

[0043] Example 9 includes the method of example 1, where the continuous phase comprises water.

[0044] Example 10 includes the method of example 3, where forming the colloidal suspension comprises forming a ferrofluid comprising a viscosity of between about 1.05 cP to about 7.0 cP.

[0045] Example 11 includes the method of example 3, where forming the colloidal suspension comprises forming a ferrofluid comprising a pH of between about 8.0 to about 8.5, and a susceptibility of between about 0.26 to about 0.32.

[0046] Example 12 includes the method of example 1, where the additional amount of the continuous phase is less than about half the amount of the dried ferrofluid.

[0047] Example 13 is a method of concentrating a ferrofluid material, which includes providing a ferrofluid, where the ferrofluid comprises a plurality of magnetic nanoparticles, a surfactant and a continuous phase, and where the ferrofluid comprises a first density. The method further includes removing at least a portion of the continuous phase from the ferrofluid, where the ferrofluid is at least partially dried. Thereafter, the method also includes mixing the at least partially dried ferrofluid with an additional amount of the continuous phase, where a ferrofluid slurry is formed. The ferrofluid slurry comprises a second density (which, is, in some examples, of a greater density than the first density).

[0048] Example 14 includes the method of example 13, and further includes filtering the ferrofluid prior to removing a portion of the continuous phase.

[0049] Example 15 includes the method of example 13, where removing at least a portion of the continuous phase comprises removing substantially all of the continuous phase, and where mixing the substantially dry dried ferrofluid comprises ball milling the dried ferrofluid material.

[0050] Example 16 includes the method of example 13, where the plurality of magnetic nanoparticles comprises a plurality of iron oxide nanoparticles.

[0051] Example 17 includes the method of example 13, where the first density comprises between about 1.01 g/cm3 to about 1.40 g/cm3.

[0052] Example 18 includes the method of example 13, where the second density comprises between about 1.01 g/cm3 to about 1.80 g/cm3.

[0053] Example 19 includes the method of example 13, where drying the ferrofluid comprises freeze drying the ferrofluid.

[0054] Example 20 includes the method of example 13, where drying the ferrofluid comprises spray drying the ferrofluid.

[0055] Example 21 includes the method of example 13, further comprising forming a colloidal suspension by ball milling the ferrofluid slurry, where the colloidal suspension comprises the second density.

[0056] Example 22 is a composition comprising a plurality of magnetic nanoparticles, a surfactant, and a solvent, where a density of the magnetic nanoparticles in the ferrofluid comprises between about 1.0 g/cm3 and about 1.8 g/cm3.

[0057] Example 23 includes the composition of example 22, where the viscosity is between about 1.05 cP and about 7.0 cP.

[0058] Example 24 includes the composition of example 22, where the pH is between about 8.0 and about 8.5. [0059] Example 25 includes the composition of example 22, where the peak susceptibility Peak Susceptibility comprises between about 0.26 and about 0.32.

[0060] Example 26 includes the composition of example 22, where the material is capable of being freeze dried and stored at about 25 degrees Celsius for about 1 year.

[0061] Example 27 includes the composition of example 22, where the solvent comprises water.

[0062] Example 28 is a system for separating at least one target from a sample suspended in a ferrofluid, the system includes a concentrated ferrofluid including a sample containing at least one target particle, where the ferrofluid comprises a density of between about 1.1 g/cm3 and about 1.2 g/cm3, a microfluidic channel having an inlet, and at least one outlet, where the inlet is configured to receive the ferrofluid, a plurality of electrodes traversing at least a portion of the microfluidic channel length and generating a magnetic field pattern along the microfluidic channel length when a current is applied to at least one of the plurality of electrodes; and where the magnetic field pattern is configured to separate the at least one target as the at least one target flows along at least a portion of the microfluidic channel length.

[0063] Example 29 includes the system of example 28, where the ferrofluid comprises a peak susceptibility between about 0.19 to about 0.41.

[0064] Example 30 includes the system of example 28, where a ratio of ferrofluid particles to the sample comprises between about 1 :2 to about 1 :3.

[0065] Example 31 includes the system of example 28, where the sample comprises living cells.

[0066] Example 32 includes the system of example 28, where the at least one target is separated from the sample based on one or more characteristics of the at least one target.

[0067] Example 33 includes the system of example 28, where the at least one target is separated from the sample by directing the at least one target to a selected outlet or trapping the at least one target based on a spacing of at least two electrodes of the plurality of electrodes.

[0068] Example 34 includes the system of example 31, where the at least one target is separated from the sample based on a characteristic of the at least one target selected from the group consisting of target size, target shape, and target elasticity. [0069] Example 35 is a method of forming a concentrated ferrofluid, and includes providing a ferrofluid comprising a plurality of magnetic nanoparticles, a surfactant and a continuous phase, and where the ferrofluid includes a first density. The method also includes removing at least a portion of the continuous phase from the ferrofluid, by drying (at least partially), resulting in a ferrofluid slurry including a second density.

[0070] Example 36 includes the method of example 35, where drying the ferrofluid comprises evaporating a portion of the continuous phase of the ferrofluid.

[0071] Example 37 includes the method of example 35, where drying the ferrofluid comprises using a pressurized filtering process to remove a portion of the continuous phase of the ferrofluid.

[0072] Example 38 includes the method of example 35, where drying the ferrofluid comprises utilizing polyethylene glycol to absorb a portion of the continuous phase of the ferrofluid.

[0073] While the principles of the disclosure have been illustrated in relation to the exemplary embodiments shown herein, the principles of the disclosure are not limited thereto and include any modification, variation or permutation thereof.

[0074] Example embodiments of the devices, systems and methods have been described herein. As noted elsewhere, these embodiments have been described for illustrative purposes only and are not limiting. Other embodiments are possible and are covered by the disclosure, which will be apparent from the teachings contained herein. Thus, the breadth and scope of the disclosure should not be limited by any of the above-described embodiments but should be defined only in accordance with claims supported by the present disclosure and their equivalents. Moreover, embodiments of the subject disclosure may include methods, systems and devices which may further include any and all elements from any other disclosed methods, systems, and devices, including any and all elements corresponding to ferrofluid concentration methods and systems utilizing the embodiments included herein. In other words, elements from one or another disclosed embodiment may be interchangeable with elements from other disclosed embodiments, resulting in yet further embodiments. In addition, one or more features/elements of disclosed embodiments may be removed and still result in patentable subject matter (and thus, resulting in yet more embodiments of the subject disclosure). Correspondingly, some embodiments of the present disclosure may be patentably distinct from one and/or another reference by specifically lacking one or more elements/features. In other words, claims to certain embodiments may contain one or more negative limitations to specifically exclude one or more elements/features resulting in embodiments which are patentably distinct from the prior art which include such features/elements.