DEVICE AND METHOD FOR COLLECTING A SAMPLE FROM A WET

ENVIRONMENT

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from and the benefit of United States Provisional Application No. 61/025,108 filed on January 31, 200S which is incorporated herein by reference in its entirety. MICROFICHE APPENDIX [0002] Not applicable.

TECHNICAL HELD

[0003] This application relates to environmental monitoring in general, and to a device and method for collecting amounts of a component in a liquid environment or wet sediments and soils in particular. BACKGROUND OF THE INVENTION

[0004] Devices and methods exist for measuring contaminant concentrations in situ at a site being studied. Currently, the two most popular in situ methods for measuring trace metal contaminants include: 1) Peepers (based on dialysis) and 2) Diffusive Gradients in Thin Films ("DGT').

[0005] In Peepers devices, metals diffuse from a bulk solution through a membrane into a solution of deionized water until equilibrium is established. Although the main analytical goal of the Peepers device is the measurement of free metal ion concentration, it is not completely selective, as many other small metal species can also diffuse through the membrane. Furthermore, Peepers' devices may not function well at concentrations due to the lack of a concentration step.

[0006] The DGT device was developed by researchers at Lancaster University (UK) and is sold by DGT Research. The DGT device utilizes a three-layer system consisting of a resin-impregnated hydrogel layer, a porous polyacrylamide hydrogel diffusive layer, and a filter membrane in a housing. A component in a bulk solution being sampled (such as a labile metal) diffuses across the filter membrane and gel layers, and is concentrated in the resin.

[0007] The diffusive layer of the DGT device is indicated generally at 100 in FIG. 1. The diffusive layer is macroscopic in scale, meaning that the cross sectional radius R of the diffusive layer is larger than the thickness of both the boundary layer δ and the reaction layer μ. Since the diffusive layer is macroscopic, the resulting boundary layer is planar; hence, the components in a bulk solution diffuse through the boundary layer δ under laminar flow.

[0008] The thickness o£ the boundary layer also controls the analytical timescale of measurement; hence, it is a critical parameter in defining a metal species that is collected and measured. The metal species can be characterized by the physiochemical parameters that define lability (and hence bioavailability) at an interface: rate constants (reactivity), stability constants (thermodynamic stability), and diffusion coefficients (mobility).

[0009] DGT suffers from a number of analytical problems associated with the hydrogel which limit the accuracy of the measurements: 1) measurements in pristine natural waters with low ionic strength (< 2 * 10- ⁴ mol/L) give spurious results which have been attributed to interactions of the trace metals being collected with

the hydrogel; 2) labile metal concentrations are underestimated under conditions of low convection (e.g. in a marsh, pond or lake) because the size of the diffusive boundary layers becomes significantly larger than the actual thickness of the hydrogel; 3) the accuracy of the measurements relies on knowledge of the diffusion coefficients of the measured species within the hydrogel, which often are not well- known; and 4) the hydrogel is itself contaminated with metals,

SUMMARY OF THE INVENTION

[0010] According to one aspect, the present invention relates to a method of conducting an environmental assay comprising the steps of: a) providing a substrate coated with a micropattern; b) contacting the micropattern with an environmental sample or chemical sample containing at least one target component, wherein the substrate or micropattern is capable of retaining the at least one target component; and c) determining the presence or absence of the at least one target component in the substrate or micropattern.

[0011] In one embodiment, the presence or absence of the at least one target component in the micropattern is determined by contacting the micropattern with a trap component that reacts with or binds to the at least one target component to produce a reaction product or bound target component, and determining the presence or absence of the reaction product or bound target component, wherein the presence of reaction product or bound target is indicative of the presence of the at least one target component in the sample.

[0012] In another embodiment the present invention relates to a method of conducting an environmental assay comprising the steps of providing a substrate coated with a micropattem having at least two orderly spaced pores each forming a discrete channel, wherein the substrate is impregnated with a trap component that reacts with or binds to at least one target component; contacting the micropattem with an environmental sample or chemical sample, wherein the least one target component from the sample diffuses exterior to each of the pores, within a boundary layer around each pore, and wherein the trap component reacts with or binds to the at least one target component to produce a reaction product or bound target component; and determinirig the presence or absence of the reaction product or bound target component wherein the presence of the reaction product or bound target is indicative of the presence of the at least one target component in the sample.

[0013J In yet another embodiment, the present invention relates to a method of conducting an environmental assay comprising the steps of providing a substrate coated with a micropattem having at least two orderly spaced protrusions, wherein the micropattem is impregnated with a trap component that reacts with or binds to at least one target component; contacting the micropattem with an environmental sample or chemical sample, wherein the least one target component from the sample diffuses exterior to each of the protrusions, within a boundary layer around each protrusion, and wherein the trap component reacts with or binds to the at least one target component to produce a reaction product or bound target component; and

determining the presence or absence of the reaction product or bound target component wherein the presence of the reaction product or bound target is indicative of the presence of the at least one target component in the sample. [0014] According to another aspect, the present invention relates to a device for collecting an environmental component in a liquid or wet sediments and soils, the device comprising at least two micrσscale diffusion pathways and a material in contact with the diffusion pathway and arranged to bind the target component which is diffused along the pathway. Each diffusion pathway comprises a boundary zone defined by a boundary layer, wherein the boundary layers do not intersect. In one embodiment, the pathway includes a pore and the material that binds the target component is a substrate.

[0015] In another embodiment, the pathway does not include a pore and the material that binds the target component is a micropattern mask. [0016] In another aspect of the present invention,, there is provided a method of conducting an environmental assay or chemical assay by depositing a thermocurable or photocurable polymer micropattern on a substrate, contacting the polymer micropattern with an environmental or chemical sample such that a target component can be retained, and determining the presence or absence of the target component in the micropattern.

[0017] Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of

specific embodiments of a device for collecting a sample in conjunction with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawing figures, wherein:

[0019] FIG.1 is a schematic diagram of a prior art macroscale system;

[0020J FIG. 2 is a schematic diagram of microscale systems according to the present invention;

[0021] FIG.3 is an exploded view of a device according to the present invention;

[0022] FIG. 4 is a schematic cross-section of a diffusion disc according to the present invention;

[0023] FIG. 5 is a schematic diagram of an enlarged surface pore pattern according to the invention; and

[0024] FIG. 6 is an assembled view of the device of FIG. 3.

[0025] Like reference numerals are used in different figures to denote similar elements.

DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention relates to a device for collecting a sample of a component from a liquid solution into which it is placed. The sample can also be collected from wet sediments and wet soils. The liquid solution can be, for example, an aquatic body such as a fresh water stream where the component being collected is a metal. However, it will be understood by persons skilled in the art that the

present invention is equally applicable to the detection and determination of organic components such as pesticides.

[0027] Referring to FIG. 3, in one embodiment, a device according to the present invention includes a housing indicated generally at 2 which includes a base 4, disk 6, o-ring 8, and cap 10. The base 4 is a disk made of plastic or other suitable material and includes a threaded outside wall 12 and a flat disk backing surface 14. [0028] The disk 6 is designed to collect metal "M" and can be an Empore™ chelating solid phase extraction disk manufactured by 3M to which a coating has been applied as described below. The cross-section of the disk 6 is shown schematically in FIG. 4 and includes a substrate 16 and a coating 18. Areas of the substrate 16 without the coating 18 form holes that define the pores 106, and the pores are regularly spaced in an orderly fashion to create a pattern. [0029] The o-ring 8 is made of elastomeric or other suitable material. [0030] The cap 10 includes an opening 20 defined by a rim 22 and a threaded inner surface (not shown) for engaging the threads 12 of the base 4 to secure the cap 10 to the base 4.

[0031] In the assembled state shown, in FIG. 6, the cap 10 is screwed onto the base 4 with the disc 6 pressed against the surface 14 and the o-ring 8 seated in the cap 10. [0032] FIG. 4 shows a cross-section of the disk 6. The substrate 16 for the disk 8 is the Empore™ extraction disk referred to above. The disk 6 includes a coating 18 on the surface of the substrate 16. There are areas of the substrate 16 without the coating 18 which define pores 106. Preferably, the thickness of the coating 18 is

about the diameter of the pores 106 such that the diffusive layer is created outside of the coating in the medium. As such, the membrane itself is not diffusion-limiting. It is unfavourable for the pore channel to be significantly thicker than the diameter of the pores as this would render the diffusion layer 108 to be within the pore. [0033] The pores 106 in the coating 18 form a microscale membrane having a surface pattern as shown in FIG. 5. Each pore size has its own characteristic detection window. It will be understood by those skilled in the art that the microscale pore size can be selected depending upon the component being collected. [0034] The size of the pores can be varied but the radius of each pore 106 is chosen such that the boundary zone is defined by a spherical boundary 108. Without being bound by theory, in the bulk solution outside of the boundary zone,, convection dominates. Within the boundary zone, diffusion dominates and the solution is substantially stagnant.

[0035] With reference to FIGS. 2 and 4, situated between the boundary layer 108 and the pore 106 is a reaction zone defined by reaction layer 110 of thickness μ. Within the reaction zone, the lifetime of M is significant. The M components can then flow freely through the pore 106 and become bound to the substrate 16. [0036] As shown in FIG. 2, the radius R of the pores can be smaller than the width 6 of the spherical boundary layer 108 and larger that the width of the reaction layer μ or smaller than both the width δ of the boundary layer 108 and the width μ of the reaction layer 110. The reaction layer 110 may or may not be spherical (i.e. it may be planar). In both embodiments, R defines the radius of a microscopic pore 106.

[0037] When R becomes smaller than δ, the boundary layer 108 becomes spherical. Hence, the lability of the target component as compared with the macroscopic case decreases since R < 5M _L - This is the consequence of the radial diffusion in which diffusion is more effective than the prior art laminar diffusion in a macroscopic system shown in FIG. 1.

[0038] When R becomes smaller than μ, the reaction layer 110 also becomes spherical. The lability increases since the reaction layer 110 also becomes spherical and hence more effective.

[0039] R can range from 1 μm to 500 μm but preferably ranges from 10 μm to 200 μm, and more preferably is about 30 μm.

[0040] In one embodiment, the component can be a metal or an organic compound. Referring to FIG. 2, the present invention uses a diffusion layer having microscale pores (a representative example of which is indicated by 106) where R is smaller than δ in one embodiment and where R is also smaller than μ in another embodiment (both referred to herein as a microscopic system). [0041] In a preferred embodiment the target components from the sample diffuse within each diffusive boundary layer outside each pore of the micropattern mask, travel through the pores, and bind to the substrate. Alternatively in another embodiment, the pores in the micropattern can be replaced with protrusions in the micropattern that are spaced similarly to the pores. In such an embodiment, the target components diffuse within each diffusive boundary layer outside each protrusion of the micropattern and bind to the micropattern itself,

[0042] A trap component can also be used that reacts with or binds to the target component. The trap component can first be bound to the binding material, namely the substrate or micropattern, before the micropattern comes into contact with the environmental or chemical sample. Alternatively, the trap component can be impregnated in the substrate or micropattern.

[0043] While the embodiment described above is directed to collecting samples of a free metal ion in a fresh water stream, other aquatic environments such as sea water can be sampled. In addition, organic compounds can be collected. It will be understood by those skilled in the art that different substrates have varying affinities for binding different compounds and that an appropriate substrate 16 is chosen for the disk 6 depending on the compound being collected.

[0044] In the microscopic regime, the size and shape of the boundary layer are governed by the dimension of the binding phase, which becomes the critical parameter for defining the nature of the diffusional mass transport and determining labile metal species.

[0045] Various patterns of surface pores, or alternatively, surface protrusions, can be used. It is preferable that the spherical boundary layers do not touch or intersect one another. In one embodiment, the pattern formed by the surface pores or protrusions is a matrix of equally spaced pores or protrusions arranged in rows as shown in FIG. 5. In another embodiment (not shown), a different pattern can be formed by orienting the pores 106 in a pattern of concentric circles and having the

pores 106 sufficiently spaced apart from each other such that each spherical boundary layer 108 at each pore or protrusion does not overlap with one another. [0046] In another embodiment, the substrate 16 can be coated with more than one layer of micropattern. As an example, there may be a first layer situated between the substrate and a second layer of micropattern, whereby the pores or protrusions of the first layer differ in size from the pores or protrusions of the second layer. For example, the first layer can have pores that are larger than the pores of the second layer. Preferably, the patterns formed by the pores or protrusions of both layers are the same.

[0047] The process for controlling the size, shape and arrangement of surface patterns can follow standard lithographic techniques, patterning the masking layer with, for example, photolithographic techniques, and etching or dissolving the masking layer away selectively without damaging the underlying disk. ¹ [0048] Alternatively, a patterned layer can be deposited directly in accordance with methods well known in the art, by microcontact printing of a thermocurable or photocurable polymer using an elastomer stamp with the desired pattern. ² A typical method comprises coating the stamp with the polymer, followed by blotting the stamp and pressing the stamp onto the disk. Once the stamp is removed, a polymer layer results which is then cured in an oven, on a hot plate, or with UV light. In addition to the prior art methods described herein, the polymer coating can be made according to the methods described in the Provisional Application

[0049] The elastomeric stamp can be made by pouring a silicone polymer, such as polydimethylsiloxane, into a mold which contains a raised pattern. It will be understood by one skilled in the art that the pattern will correspond to the inverse of the micropattemed stamp. The mold can also be formed with recesses. [0050] The mold is optionally produced by high-resolution laser or inkjet printing onto acetate sheets, by photolithography, or by electron-beam or scanning-probe lithography in accordance with methods well known in art.

[0051] In use, a device according to the present invention is immersed into a stream to detect heavy metals which bind to the thiol functionalized first channel. The presence of heavy metals is readily detected using Raman spectroscopy, electrochemical means or the metals are optionally removed from the device and analyzed using atomic spectroscopy.

Citations Referred to in Specification

₁ . Wang et al-, Anal Chem (2005) 77, 7539.

₂ . Gates et al., Chem Rev (2005) 105, 1171.

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