WO2010022324A2

WO2010022324A2 - Methods of patterning paper

Info

Publication number: WO2010022324A2
Application number: PCT/US2009/054601
Authority: WO
Inventors: Andres W. Martinez; Scott T. Phillips; Benjamin Wiley; George M. Whitesides
Original assignee: President And Fellows Of Harvard College
Priority date: 2008-08-22
Filing date: 2009-08-21
Publication date: 2010-02-25
Also published as: WO2010022324A3

Abstract

Methods of patterning hydrophobic materials onto hydrophilic substrates are described. Also described are articles comprising a hydrophilic substrate impregnated with a hydrophobic material, and a transparent layer capable of being patterned in contact with one surface of the substrate.

Description

METHODS OF PATTERNING PAPER

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 61/090,997, filed August 22, 2008, the entire contents of which are hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

[0002] Paper microfluidic devices are a promising technology for applications in which low cost and simplicity of fabrication must be combined with complex microfluidic function (Martinez et al., Angew. Chem. Int. Ed. Engl. 46:1318-1320 (2007); Martinez et al., Anal. Chem. 80:3699-3707 (2008)). These applications include diagnostic devices for the developing world, devices for use in drug development, and tools for monitoring the quality of water and the environment (Daar et al., Nat. Genet. 32:229-232 (2002); Mabey et al., Nat. Rev. Microbiol. 2:231-240 (2004); Chin et al., Lab. Chip. 7:41-57 (2007)). These devices combine many of the useful characteristics of microfluidic devices made out of poly(dimethyl siloxane) and glass (e.g., they use microliter volumes of fluids and measure multiple assays simultaneously) (Sia et al., Electrophoresis 24:3563-3576 (2003)) with the capabilities of dipsticks and lateral- flow assays (e.g., they wick fluids by capillary action, adsorb reagents, filter samples, and are easy to dispose of by incineration) (Chin et al., Lab. Chip. 7:41-57 (2007); von Lode, Clin. Biochem. 38:591-606 (2005)). Paper-based microfluidic devices are thus a new class of microfluidic systems that generate high-technology function from low-technology materials.

SUMMARY OF THE INVENTION

[0003] The invention is based, at least in part, on the discovery of a rapid, simple, and inexpensive method, termed "FLASH" (Fast Lithographic Activation of Sheets). In some embodiments, FLASH is used for laboratory prototyping of microfluidic, paper-based analytical devices (μPADs). The method produces μPADs in less than about 30 min (from design to completion) using an ink-jet printer, a source of UV light (a UV lamp or sunlight), and a hot plate (when the UV lamp is used). The method is compatible with small pieces of paper (e.g., about 0.5 in²) as well as large (e.g., about 8.5 in x about 11 in), and produces hydrophilic features in paper with dimensions as small as about 200 μm that are demarcated by hydrophobic barriers of a hydrophobic polymer, such as SU-8 photoresist (as small as about 200 μm); the hydrophobic barriers extend through the thickness of paper (in the z-direction), and produce microfluidic channels that are capable of distributing fluids by capillary action.

[0004] Accordingly, in one aspect, the invention features a method of patterning a hydrophilic substrate, e.g., paper. The method includes contacting at least a portion of the hydrophilic substrate with a hydrophobic material, e.g., photoresist; covering one face of the substrate with an adhesive transparent or translucent layer; disposing a pattern onto the transparent or translucent layer, e.g., using a printer, photocopier, a pen, or a stamp; and curing the hydrophobic material, e.g., by subjecting the substrate to light (such as UV light or sunlight). [0005] In another aspect, the invention features an article comprising a hydrophilic substrate impregnated with a hydrophobic material, e.g., photoresist, and a transparent or translucent layer in contact with one surface of the substrate. In some embodiments, the article further comprises an adhesive layer disposed between the substrate and the transparent or translucent layer, whereby the transparent or translucent layer is affixed to the substrate. In some embodiments, the article is provided in a kit, which can further include instructions for applying a pattern to the transparent or translucent layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The subject matter is described with reference to the Drawings, which is provided for the purpose of illustration only and is not intended to be limiting of the invention.

[0007] Figure 1. Procedure for FLASH fabrication of microfluidic devices in paper. A) Schematic of the method. B) Designs for microfluidic channels were printed directly onto FLASH paper (using Whatman Chromatography paper No. 1). C) FLASH paper was exposed to UV light. D) The photoresist-impregnated paper was removed from the transparency film and black construction paper. E) The paper was baked on a hotplate. F) After developing the paper in acetone and 70% isopropyl alcohol, the microfluidic devices are ready for use. The dotted lines indicate the edges of the paper.

[0008] Figure 2. A) A μPAD made from Whatman Chromatography paper No. 1 designed to measure the smallest functional hydrophilic channel. A large sample reservoir leads into a series of channels of decreasing widths (from 500 μm to 50 μm). B) The device shown in (A) after adding 40 μL of 1 mM erioglaucine to the sample reservoir. The aqueous dye filled the channels as small as 250 μm in width for chromatography paper. C) A μPAD designed to measure the smallest functional hydrophobic barrier. A large sample reservoir leads into a series of channels that contain hydrophobic barriers of decreasing widths (from 500 μm to 50 μm). D) The device shown in (C) after adding 40 μL of 1 mM erioglaucine. The aqueous dye crossed the barriers that were less than 200 μm in width.

[0009] Figure 3. Micro-PADs produced using chromatography paper by (A) printing the pattern with an ink-jet printer, (B) printing the pattern with a photocopy machine, and (C) drawing the pattern through a stencil using a waterproof black pen. (D) A μPAD patterned using sunlight. Micro-PADs from (E) Technicloth, or (F) a paper towel. The devices were filled with an aqueous blue dye (1 mM erioglaucine)

DETAILED DESCRIPTION

[0010] The methods described herein involve patterning of hydrophobic materials onto hydrophilic substrates, e.g., paper, using FLASH. Such patterned substrates can be used, e.g., in diagnostic assays (e.g., as described in Martinez et al, Angew. Chem. Int. Ed. Engl. 46:1318-1320, 2007; and PCT/US07/081848). [0011] The methods described herein include lithographic methods for prototyping microfluidic devices in paper. The method is rapid, inexpensive, requires no specialized equipment, and can be performed in any laboratory; clean rooms commonly associated with photolithography are not necessary. [0012] We anticipate that microfluidic devices fabricated in paper will be useful in developing countries, such as innovative developing countries "IDC's (for monitoring the health of large populations that do not have access to centralized medical facilities), and in industrialized countries (for monitoring chronic diseases, for military applications, and for applications in environmental monitoring, agriculture, veterinary medicine, and homeland security). [0013] The methods of patterning described herein are convenient ways of producing μPADs, especially when the FLASH paper is prepared in advance. The methods requires less than about 30 min to pattern an 8.5 in. x 11 in. piece of FLASH paper (about 10 min to print the pattern using an inkjet printer, about 6 min to expose and bake the paper, and about 10 min to develop and dry the paper). When using a photocopying machine to print the patterns, less than about 20 min are required to pattern a single piece of FLASH paper, but additional FLASH paper can be processed in minutes; the photocopying machine allows for much higher throughput than an inkjet printer. The materials used to prepare an 8.5 in. x 11 in. sheet of FLASH chromatography paper cost less than about $1.6 per sheet: about $0.40 of photoresist, about $0.27 of paper, about $0.84 of transparency film, and about $0.04 of black paper. The cost of the materials per device is about 1-3 cents depending on the size of the device.

[0014] Some of the methods are used for prototyping μPADs, and to make available a method that is capable of shifting the development stages for diagnostic devices from developed countries to those regions where they are needed most. A prototyping method that is widely available should lead to unexpected uses of μPADs, and should motivate the development of new photoresists that provide additional and exciting function to paper-based microfluidic devices. Extensions of FLASH patterning should be compatible with reel-to-reel processes for manufacturing in bulk.

Fast Lithographic Activation of Sheets ("FLASH" Method)

[0015] The methods described herein can be used for producing paper-based devices rapidly for minimal cost. In some applications, the methods are used to prototype paper-based devices in a way that is accessible to a wide variety of laboratories for minimal cost.

[0016] Fig. IA schematically illustrates one method for FLASH patterning a hydrophilic, porous substrate, e.g., paper, with a hydrophobic material. In this example, the method involves: (i) impregnating paper with SU-8 photoresist; (ii) drying the paper to remove propylene glycol monomethyl ether acetate (PGMEA) from the paper (PGMEA is the solvent in the photoresist formulation); (iii) covering one face of the impregnated paper with an adhesive transparency film and the other face with black construction paper; (iv) printing a pattern onto the transparency film using an ink jet printer, a photocopying machine, or a pen; (v) exposing the paper to UV light using an Intelliray 600 UV lamp or sunlight; (vi) removing the transparency and black paper backing; (vii) baking the paper to polymerize the SU-8 photoresist (no baking step is required if sunlight is used for the exposure step); and (viii) removing unpolymerized resist (the sections not exposed to UV light) by washing the paper with acetone and isopropyl rubbing alcohol (70% propan-2-ol, 30% water).

[0017] In some embodiments, steps (i) to (iii) of this process are performed independently of steps (iv) to (vii), and are used to produce an article termed "FLASH paper" (transparency-covered, photoresist-impregnated paper). FLASH paper can be prepared in bulk quantities and stored in the absence of light for more than about 6 months before use. FLASH paper can subsequently be used for patterning devices. The photoresist in FLASH paper is dry and there are no odors. [0018] The transparency layer can be patterned using any method for disposing patterns onto the layer. For example, an ink-jet printer or photocopier can be used. In other examples, a pattern can be drawn by hand using a waterproof black pen.

Patterning Hydrophilic and Hydrophobic Channels in Paper

[0019] Micro fluidic channels in paper require that the patterned hydrophobic polymer extend through the entire thickness of the paper, otherwise the aqueous fluid escapes the channel and spreads through the device. The requirement that the channel-forming polymer extend through the full thickness of the paper can limit the methods available for patterning paper on a laboratory scale: printing methods using standard inks, for example, are not suitable for making channels in paper because inks are designed to remain on the surface of paper, not to absorb into it. Another limitation is the structure of paper itself: paper is composed of intertwined fibers that are oriented in the x,y-plane of a sheet of paper, and that are stacked on top of one another in the z-direction (Giddings et al., Advances in Chromatography; Marcel Dekker: New York, 1965). The result of this arrangement is that spreading of liquids is faster in the x-, y-plane than in the z-direction; this anisotropy in rates of spreading leads to blurring of the patterns. Appropriate choices of monomers, polymers, and solvents can overcome these characteristics of paper, and to enable the patterning of distinct features that pass through the entire thickness of paper. [0020] In some embodiments, photolithography is used to pattern paper. Potential problems with creating well-defined patterns in paper can be overcome by impregnating an entire sheet of paper with photoresist. The photoresist can be selectively polymerized in the paper by exposure to UV light through a transparency mask (such as black ink printed on the transparency film). The unexposed photoresist can be removed by washing, and the remaining polymerized photopolymer can extend through the thickness of the paper.

Hydrophilic Substrates

[0021] Any porous, hydrophilic substrate can be used in the methods described herein, and the choice of substrate can be dictated by the contemplated application. For example, paper is a known platform for biological assays and diagnostic devices. Paper is an inexpensive and porous matrix. Solutions can be adsorbed by paper and moved around the paper by capillary action. Liquid movement within paper and related porous matrices serves as a foundation for many existing applications (e.g., portable assays, diagnostic devices, chromatography, blots, etc.). Liquid movement within paper can be controlled if paper is equipped with patterned hydrophobic features. This patterning has been demonstrated previously using photolithography techniques (see, e.g., Martinez et al., Angew. Chem. Int. Ed. Engl. 46:1318-1320, 2007; PCT/US07/081848). Further, positional control of wetting allows for fabrication of complex micro fluidic paper-based devices for bioassays and diagnostics (see, e.g., Martinez et al., Angew. Chem. Int. Ed. Engl. 46:1318- 1320, 2007; PCT/US07/081848).

[0022] While many of the embodiments described herein include the use of paper as the porous, hydrophilic substrate, any substrate that adsorbs hydrophilic solutions can be used, e.g., nitrocellulose and cellulose acetate, filter paper, cloth, porous polymer film, and glass fiber paper.

Hydrophobic Materials

[0023] The patterning techniques described herein can be used to pattern many types of hydrophobic materials onto the paper. For example, the hydrophobic material can be photoresist, PDMS, poly(lactic-co-glycolic acid), epoxy, polystyrene, or liquid polybutadiene based elastomeric oligomers (such as those from Sartomer Co., Exton, PA). Other hydrophobic materials that can be used include, without limitation, any plastic that can be soluble in organic solvents (e.g., polystyrene and derivatives, polyethers, polyamides, PMMA, polycarbonate, polyethylene, polypropylene, photoresist precursors (e.g., SU8), waxes and fats), and/or that can be made by, e.g., polymerization of poly condensation from organic solvents at, e.g., 20-70° C (e.g., PDMS, polyurethane and epoxy derivatives, phenol- formaldehyde polymers or acrylate and matecrylate derivatives such as poly(methyl methacrylate-co-2-hydroxylethyl methacrylate)). Preferably, the hydrophobic material is a photocurable hydrophobic material.

[0024] In one or more embodiments, the hydrophobic material is photoresist. Some paper-based microfluidic devices described herein contain hydrophilic channels with feature sizes greater than about 100 μm, and more commonly, feature sizes ranging from about 250 μm to about 2000 μm (these dimensions allow visual readout of colorimetric assays carried out on the paper). Commercial photoresists are designed to produce features on silicon wafers with sizes less than 1 μm and with well-defined edges and thicknesses (Shaw et al., IBMJ. RES. DEVELP. 41 :81-94 (1997); U.S. Patent No. 6,391,523). In paper, the thickness of the features is defined by the thickness of the paper, and expensive commercial photoresists are unnecessary for this application. Instead, an epoxy-based negative photoresist can be formulated from commercially available reagents for about $65/kg (approximately 6 g or $0.40 of photoresist are required to pattern a 20 cm x 20 cm sheet of Whatman Chromatography paper No. 1). In some examples, the photoresist is composed of EPON SU-8 resin (52% by mass), triarylsulfonium hexafluorophosphate salts (photoacid) (5% by mass), and PGMEA (43% by mass) (Shaw et al, IBMJ. RES. DEVELP. 41 :81-94 (1997); U.S. Patent No. 6,391,523 Bl).

Source of UV Light

[0025] Any source of UV light can be used to polymerize photoresist in paper so long as the photon flux is high enough to penetrate through the thickness of the paper. For example, a 600 W metal halide lamp (UVitron Intelliray 600) can be used for this purpose. This lamp delivers high intensity (about 100 mW/cm²), long wave (365 nm) ultraviolet light that requires exposure times of only about 6-14 s in the exemplary articles described herein. Alternatively, sunlight can be used to pattern paper.

Applications

[0026] The methods described herein can be used to provide patterned substrates, e.g., paper, that can be used in a number of applications. For example, the methods described herein can be used to produce paper-based diagnostics (such as described in PCT/US07/081848). One particular application is to prototype paper-based diagnostics. In some examples, the transparent layer is adhered to the substrate over a significant portion of its surface area, e.g., more than 70%, 80%, 90%, or 95% of the surface area of the transparent layer. Such a configuration allows the production of large FLASH paper containing tens, hundreds, or even thousands of diagnostics on a single sheet of FLASH paper. The use of an adhesive to contact a transparent layer to a substrate is advantageous over other methods, such as clamping, and allows the production of multiple diagnostics. These multiply produced devices can be the same, or they can differ in one or more aspect to produce prototypes that can be tested for a particular diagnostic application. [0027] In some aspects, FLASH paper can be used as a toy, for example, as an alternative to Sun Print Paper; to produce coloring books (by pattering paper and then adding a coloring agent, such as food coloring, to the patterns); or to produce "spy" paper (where FLASH paper is patterned with a secret message that is displayed by developing the paper and adding colored dye).

EXAMPLES

Example 1 - Preparation of FLASH Paper

[0028] UV light-sensitive photoresist was prepared by combining EPON SU-8 resin (13O g, Hexion Specialty Chemicals) with propylene glycol methyl ether acetate (PGMEA) (134 mL, Sigma-Aldrich) in a glass jar, and stirring the mixture on a stir plate for 48 h at room temperature until the resin was completely dissolved. A 50% solution of mixed triarylsulfonium hexafluorophosphate salts in propylene carbonate (20 mL, Sigma-Aldrich) was added to the dissolved resin and stirred for an additional hour. The photoresist was stored at room temperature in a sealed jar covered with aluminum foil.

[0029] Photoresist was poured onto a piece of paper and the photoresist was spread evenly around the paper using a wooden rolling pin. The photoresist- impregnated paper was baked on a hotplate set at 130 ⁰C for about 5-10 min to evaporate the PGMEA from the photoresist.

[0030] The paper was allowed to cool to room temperature. The paper was then covered with an adhesive transparency film (Computer Grafix clear adhesive backed ink-jet film; one side of this plastic film was sticky), and this label-coated paper was placed on an 8.5 in. x 11 in. piece of black construction paper; the black paper serves as an optical filter to minimize reflected UV light when the paper is exposed (Figure IA). The three components (transparency film/photoresist-impregnated paper/black construction paper) were held together by sealing the adhesive border of the transparency to the construction paper (the photoresist-impregnated paper was about 0.5 cm smaller on all sides than the transparency and construction paper so that the transparency sheet could be adhered to the construction paper around the edges of the photoresist-impregnated paper). FLASH paper was stored at room temperature wrapped in aluminum foil.

Example 2 - Patterning Hydrophilic and Hydrophobic Channels in Paper

[0031] Designs for micro fluidic devices were prepared using CleWin (PhoeniX Software). The designs were saved as post-script files, converted to PDFs, imported into Adobe^®Photoshop^® at 600 DPI resolutions and printed directly onto the transparency face of FLASH paper using an inkjet printer (HP Deskjet D2430 set to print at maximum resolution using black ink only) (Figure IB). [0032] FLASH paper was placed in a UV light curing chamber (Unitrin Raven equipped with a Unitrin Intel-ray 600 UV lamp), with the tray in the chamber at the lowest setting. The paper was irradiated with UV light at 100% intensity. Exposure times were set according to the type of paper being patterned. The FLASH paper was removed from the chamber immediately after exposure, and the transparency film and the construction paper were removed from the photoresist-impregnated paper. The photoresist-impregnated paper was placed on a hotplate set to 130 ⁰C, baked for 5 minutes, and cooled to room temperature (Figure IC-E). [0033] The patterns were developed by soaking the paper in a bath of acetone (1 min), followed by a rinse in acetone (Ix) and a rinse in 70% isopropyl rubbing alcohol (30% water in propan-2-ol, 2x). The paper was blotted with paper towels between the two rinses with isopropyl alcohol. After the final rinse, the paper was blotted between paper towels and dried under ambient conditions (5 min) (Figure IF).

[0034] For patterning FLASH paper using sunlight instead of a UV lamp, FLASH paper was placed in direct sunlight on a flat surface for 6 min (Cambridge, MA at 12 pm, June 25, 2008). After exposure, the transparency film and the construction paper were removed from the photoresist-impregnated paper, and the photoresist-impregnated paper was developed as described above. Example 3 - FLASH Patterning Using a Photocopying Machine

[0035] FLASH paper was prepared using adhesive transparency film designed for photocopying machines instead of inkjet printers. FLASH paper (prepared using a laser printer/copier transparency film) was loaded into the paper tray of a photocopying machine (Imagistics IM4511). The patterns were printed onto white paper using the settings described above and photocopied onto the transparency face of FLASH paper using the default settings on the photocopier. This method worked well for features about 0.5-1 mm wide (Figure 3). For smaller or larger features, the toner from the photocopying machine does not apply evenly or thick enough on the FLASH paper to block transmission of UV light. It is possible, however, to print patterns on FLASH paper with throughput of about 1 sheet per second. This method of patterning is ideal for situations where large numbers of identical devices are desired.

Example 4 - FLASH Patterning Using a Pen

[0036] Micro-PADs were produced by drawing patterns onto FLASH paper using a black pen (Sarstedt black permanent waterproof pen) and a stencil cut from a transparency sheet using a laser cutter (Universal Laser VL-300 50 Watt Versa Laser) (Figure 3C). The patterns made using this method were not as well defined as those made using a printer, and the size of the pattern depended on the pen and the skill of the technician. This method of patterning is useful for quick, proof-of- concept experiments in situations where inkjet printers or photocopying machines are unavailable.

[0037] Alternatively, if a photocopying machine is available, a hand-drawn pattern is photocopied directly onto FLASH paper. Example 5 - Resolution of the Hydrophobic and Hydrophilic Patterns.

[0038] A series of hydrophobic lines and hydrophilic channels of increasing width was patterned into Whatman Chromatography paper No.1 , ITW Technicloth, and Scott hard roll paper towel to determine the minimum-sized features that give functional barriers and channels for controlling the position of fluids in paper (Table 1, Figure 2).

[0039] Thirty microliters of 1-mM erioglaucine (aqueous blue dye) were added to the sample reservoirs of the devices shown in Figure 2 to determine the smallest functional channel and the smallest functional barrier. The dye was allowed to wick into the devices for 10 min, and excess dye was absorbed with a paper towel. The width of the smallest channel that was filled with fluid and the width of the smallest barrier that prevented fluid from crossing it were measured by imaging the patterns using a Nikon digital camera (DXM 1200) attached to a stereomicroscope (Leica MZ12). The images were analyzed using Adobe^®Photoshop^®. [0040] The smallest functional channel (defined as a channel that could wick a 1 mM aqueous solution of erioglaucine) was designed to be 200 μm in width and was measured to be 184 ± 12 μm (based on 10 measurements) (Table 1; all the dimensions are given as the average ± one standard deviation often measurements.). Smaller channels did not wick the dye. The smallest functional barrier (defined as a barrier that prevented aqueous solutions from crossing it for at least 10 min) was designed to be 200 μm in width and was measured to be 186 ± 13 μm (based on 10 measurements) (Table 1). Table 1. Summary of the experimental details and results for FLASH patterning.

Paper Cost³ Thickness PhotoPre- ExpoPost- Channel Barrier

($/m²) resist bake sure bake

(μm)

(g/ni²) (min) f Ks)J (min) (μm) (μm)

Chromato6.7 175+5 155 10 10 5 256+20 210+30 graphy 360^b 0^b 248+ 14^b 186+13^b

Technicloth 1.2 ₂₄5+₁₀ 265 10 14 5 184+12 370+18 Paper towel 0.15 70+16 120 5 8 5 214+20 242+14

These values are commercial prices for each type of paper, not bulk costs. ' FLASH paper exposed to sunlight.

Claims

CLAIMSWhat is claimed is:

1. A method of patterning a porous, hydrophilic substrate into hydrophobic and hydrophilic regions, the method comprising:

contacting the hydrophilic substrate with a hydrophobic material;

covering one face of the substrate with an adhesive transparent layer;

disposing a preselected pattern onto the transparent layer; and

curing the hydrophobic material by subjecting the substrate to UV light.

2. The method of claim 1 , wherein the hydrophobic material is cured by passing UV light through the adhesive transparent layer.

3. The method of claim 1, wherein the pattern of the hydrophilic regions are determined by the preselected pattern disposed onto the transparent layer.

4. The method of claim 1, wherein the pattern of the hydrophobic regions are determined by the inverse of the preselected pattern disposed onto the transparent layer.

5. The method of claim 1, wherein the substrate is paper, nitrocellulose, cellulose acetate, filter paper, cloth, or porous polymer film.

6. The method of claim 1 , wherein the hydrophobic material is photoresist.

7. The method of claim 1 , wherein the preselected pattern is disposed onto the transparent layer by printing or stamping.

8. The method of claim 7, wherein the preselected pattern is printed onto the transparent layer using a laser printer.

9. The method of claim 1, wherein the porous, hydrophilic substrate is patterned into an array of assay units.

10. The method of claim 9, wherein each assay unit comprises

a fluid impervious barrier comprising the hydrophobic material, the barrier substantially permeating the thickness of the porous, hydrophilic substrate and defining a boundary of an assay region within the porous, hydrophilic substrate; and

an assay reagent in the assay region.

11. The method of claim 10, wherein the barrier further defines a boundary of a channel region within the porous, hydrophilic substrate, the channel region fluidically connected to the assay region.

12. The method of claim 11 , wherein the barrier further defines a boundary of a sample deposition region within the porous, hydrophilic substrate, the channel providing a fluidic pathway within the porous, hydrophilic substrate between the sample deposition region and the assay region.

13. The method of claim 12, wherein the barrier further defines boundaries of a plurality of assay regions.

14. An article comprising a hydrophilic substrate impregnated with an uncured, photocurable, hydrophobic material, and a transparent layer in contact with one surface of the substrate.

15. The article of claim 14, wherein the article is capable of having a preselected pattern disposed onto the transparent layer.

16. The article of claim 14, further comprising a backing layer in contact with a surface of the substrate opposite the transparent layer.

17. The article of claim 14, wherein the substrate is paper, nitrocellulose, cellulose acetate, filter paper, cloth, or porous polymer film.

18. The article of claim 14, wherein the hydrophobic material is photoresist.

19. The article of claim 14, wherein the preselected pattern can be disposed onto the transparent layer by printing or stamping.

20. The article of claim 19, wherein the preselected pattern can be printed onto the transparent layer using a laser printer.