Fabrication of paper-based microfluidic devices

Fabricating a fluid testing device includes receiving a substrate, and applying a pattern of hydrophobic material to the substrate. The substrate is positioned between layers of a thermally reflective material. Heat and pressure is applied to the substrate and thermally reflective material to reflow the pattern of hydrophobic material. A protective coating is applied over a portion of the substrate to form the fluid testing device.

TECHNICAL FIELD

The present invention relates generally to a method for fabricating of paper-based microfluidic devices and an apparatus formed by the method. More particularly, the present invention relates to a method for fabricating a paper-based microfluidic device on an arbitrary substrate type and an apparatus formed by the method.

BACKGROUND

Paper-based microfluidic devices such as microfluidic paper-based analytical devices (microPADs or pPADs) offer great potential as a low-cost platform to perform chemical and biochemical tests. Examples of such tests include clinical and veterinary diagnostics, industrial and environmental testing, biochemical and pharmaceutical testing, and food/beverage quality control testing. Paper-based microfluidic devices rely on the phenomenon of capillary penetration in porous media to transport fluids through the microfluidic device. To control fluid penetration in porous substrates such as paper in two or three dimensions, factors such as pore structure, wettability and geometry of the microfluidic device are controlled in view of other factors such as viscosity and evaporation rate of the liquid to be tested. Many microfluidic devices use hydrophobic barriers on hydrophilic paper that passively transport fluids to output areas including chemical or biological reagents where chemical or biological reactions of the fluid with the reagents takes place.

Recently, significant progress has been made in the development of paper-based devices that integrate various processing steps to carry out chemical tests with minimum user interference. Hydrophobic barriers patterned in paper control the movement of liquids based on channel geometry that can carry the liquid and reagents according to predefined sequences. Three-dimensional microPADs often include an input layer on a first outer surface and an output layer on a second outer surface with one or more layers between. Three-dimensional microPADs offer more flexibility and potential for more elaborate flow sequences.

SUMMARY

The illustrative embodiments provide a method and apparatus. An embodiment of a method for fabricating a fluid testing device including receiving a substrate, applying a pattern of hydrophobic material to the substrate, and positioning the substrate between layers of a thermally reflective material. The embodiment further includes applying heat and pressure to the substrate and the thermally reflective material to reflow the pattern of hydrophobic material. The embodiment still further includes applying a protective coating over a portion of the substrate to form a fluid testing device.

In another embodiment, the protective coating is applied to the pattern. In another embodiment, the protective coating is applied to an output layer of the fluid testing device.

In another embodiment, applying the pattern of hydrophobic material to the substrate further includes depositing the pattern of hydrophobic material to the substrate using a printing device.

In another embodiment, applying the pattern of hydrophobic material to the substrate further includes receiving a transfer medium, applying the pattern of hydrophobic material to the transfer medium, aligning the transfer medium with the substrate, applying the heat and pressure to the transfer medium and the substrate to transfer the pattern of hydrophobic material to the target substrate, and removing the transfer medium from the substrate.

In another embodiment, the transfer medium is one of a plastic slide, a metal plate, a metal cylinder or other non-absorbing hydrophobic surface.

Another embodiment further includes applying a mask to hydrophilic portions of the substrate, applying an adhesive material to the substrate, the mask protecting the hydrophilic portions of the substrate from the adhesive material, removing the mask from the substrate, and aligning and positioning the substrate in contact with another substrate.

In another embodiment, the applying of the mask is performed before the applying of the protective coating. In another embodiment, the applying of the adhesive material is performed after the applying of the protective coating.

In another embodiment, the substrate includes a porous hydrophilic material capable of allowing the movement of fluids such as paper. In another embodiment, the hydrophobic material comprises a wax.

In another embodiment, the thermally reflective material comprises one or more laminated foil films.

In another embodiment, more than one layer of substrate is placed inside the thermally reflective material and separated by sacrificial absorbing material.

In another embodiment, the mask is applied after a chemical substance capable of undergoing chemical reaction upon contact with a fluid is deposited in the substrate.

An embodiment of an apparatus includes a substrate, and a pattern of hydrophobic material disposed on the substrate, the pattern of hydrophobic material being formed by applying the pattern of hydrophobic material to the substrate, positioning the substrate between layers of a thermally reflective material, and applying heat and pressure to the substrate and thermally reflective material to reflow the pattern of hydrophobic material. The embodiment further includes a protective coating disposed over a portion of the substrate to form a fluid testing device.

In an embodiment, the computer usable code is stored in a computer readable storage device in a data processing system, and wherein the computer usable code is transferred over a network from a remote data processing system.

In an embodiment, the computer usable code is stored in a computer readable storage device in a server data processing system, and wherein the computer usable code is downloaded over a network to a remote data processing system for use in a computer readable storage device associated with the remote data processing system.

DETAILED DESCRIPTION

One or more embodiments of the present invention are directed to a method for fabricating a paper-based microfluidic device on an arbitrary substrate type and an apparatus formed by the method such as porous and/or paper substrate types. Embodiments recognize that known processes for fabricating paper-based microfluidic devices typically include printing wax patterns on paper with a wax printer, and heating the paper to reflow the wax to create hydrophobic barriers. Embodiments further recognize that conventional processes further include an assembly operation in which an adhesive is indiscriminately sprayed on sheets of patterned paper to glue the layers together.

Embodiments recognize that known solutions for fabricating paper-based microfluidic devices may suffer from a number of drawbacks such as infeasibility for certain paper types, distorting of layout design during reflow, undesirable alteration of hydrophilic paper channels due to adhesive spraying, or undesirable reaction of the tested fluid during testing.

An embodiment provides for a novel process for fabricating a paper-based testing device including applying a hydrophobic material (e.g., a wax) to a substrate (e.g., paper), positioning the substrate between layers of thermally reflective material, applying heat and pressure to the substrate and layers of thermally reflective material thereby reflowing the hydrophobic material, removing the thermally reflective material, and applying a protective coating over the hydrophobic material and substrate.

Another embodiment provides for a novel process for fabricating a paper-based testing device having a patterning step including wax-printing desired geometries on a hydrophobic sacrificial layer (e.g., a transparent plastic slide), and a reflow step including placing the sacrificial layer and a target hydrophilic paper substrate in contact in an insulating thermal envelope and applying heat and pressure to transfer the hydrophobic pattern to the substrate.

In another embodiment, several patterned paper sheets are joined together through an assembly step that includes constructing a protective mask, placing the protective mask on the patterned paper layers, and spraying or applying liquid adhesive on each layer. The embodiment further includes attaching and gluing pairs of paper layers to construct a multi-layer three-dimensional (3D) paper testing device. The embodiment further includes a step in which a hydrophobic colorimetric color protection layer is applied to the final paper layer of the testing device.

Various embodiments described herein describe a multistep process to fabricate single-layer or multi-layer 3D paper-based fluid testing devices that may provide one or more advantages over known processes including, but not limited to, providing the ability to create hydrophobic barriers on arbitrary types of porous materials, providing the ability to fabricate testing devices with high reproducibility and fidelity, providing increased repeatability of reactions, increasing yield or increasing shelf-life of the testing device.

For the clarity of the description, and without implying any limitation thereto, the illustrative embodiments are described using microfluidic devices. An embodiment can be implemented with other fluid testing devices within the scope of the illustrative embodiments.

Furthermore, simplified diagrams of the example microfluidic devices are used in the figures and the illustrative embodiments. In an actual fabrication of a microfluidic device, additional structures that are not shown or described herein may be present without departing the scope of the illustrative embodiments. Similarly, within the scope of the illustrative embodiments, a shown or described structure in the example microfluidic device may be fabricated differently to yield a similar operation or result as described herein.

A specific shape or dimension of a shape depicted herein is not intended to be limiting on the illustrative embodiments. The shapes and dimensions are chosen only for the clarity of the drawings and the description and may have been exaggerated, minimized, or otherwise changed from actual shapes and dimensions that might be used in actually fabricating a microfluidic device according to the illustrative embodiments.

Furthermore, the illustrative embodiments are described with respect to a microfluidic device only as an example. The steps described by the various illustrative embodiments can be adapted for fabricating other fluid diagnostic or testing devices, and such adaptations are contemplated within the scope of the illustrative embodiments.

An embodiment when implemented in a software application causes a fabrication system to perform certain steps as described herein. The steps of the fabrication process are depicted in the several figures. Not all steps may be necessary in a particular fabrication process. Some fabrication processes may implement the steps in different order, combine certain steps, remove or replace certain steps, or perform some combination of these and other manipulations of steps, without departing the scope of the illustrative embodiments.

A method of an embodiment described herein, when implemented to execute on a manufacturing device, tool, or data processing system, comprises substantial advancement of the functionality of that manufacturing device, tool, or data processing system in fabricating microfluidic devices.

The illustrative embodiments are described with respect to certain types of devices, layers, patterning devices, reagents, substrates, hydrophobic materials, hydrophilic materials, planes, structures, materials, dimensions, numerosity, data processing systems, environments, components, and applications only as examples. Any specific manifestations of these and other similar artifacts are not intended to be limiting to the invention. Any suitable manifestation of these and other similar artifacts can be selected within the scope of the illustrative embodiments.

With reference toFIG. 1, this figure depicts a conventional process100for fabricating microfluidic devices such as according to Carrilho et al. [“Understanding Wax Printing: A Simple Micropatterning Process for Paper-Based Microfluidics”. E. Carrilho, A. W. Martinez and G. M. Whitesides. Anal. Chem. 2009, 81, 7091-7095]. In process100, a paper substrate102is received and patterns of wax104are printed on a surface of paper substrate102with a printing device. The paper is then heated by a heating device, such as a hotplate, to reflow the wax to extend through the thickness of paper substrate102to form a wax barrier106. As a result of patterning and reflow, a test zone108and channel112is defined by wax pattern110. For assembly of multilayer microfluidic devices, adhesive is indiscriminately sprayed on sheets containing multiple copies of patterned paper and the layers are stacked to glue the layers together to form to form a microfluidic device such as described by Lewis et al. [“High throughput method for prototyping three-dimensional, paper-based microfluidic devices.” G. G. Lewis, M. J. DiTucci, M. S. Baker and S. T. Phillips. Lab on a Chip 12(15):2630-3 (2012)].

During testing of a liquid, the liquid flows through channel112to test zone108which includes one or more reagents to react with the fluid to indicate a testing result. Chemical reactions that produce a colorimetric output are commonly used since they do not typically require electrical, optical, or other types of equipment to indicate the testing result.

As previously discussed, known conventional processes such as illustrated inFIG. 1may suffer from a number of drawbacks. During patterning, wax printing directly on paper is not always feasible on all substrate types such as for highly porous or very thick substrates. In addition, during the reflow process necessary to melt printed wax features and impregnate the paper thickness to create hydrophobic barriers may cause in plane diffusion that distorts the original layout design. Using hot lamination may reduce wax spread and allow more controlled fabrication, but challenges remain. Laminator heat is often not enough for reflow to impregnate the entire paper thickness, requiring several repetitions/passes. Also, excess way may damage laminator cylinders of laminating devices. Further, multiplexing several sheets may be desirable but interference may be a concern.

Further, conventional microfluidic device assembly processes involve indiscriminately spraying glue to entire patterned sheets to attach the sheets together which may cause hydrophilic paper channels to turn hydrophobic and prevent flow of fluid. In addition, during reaction of the microfluidic device with a test fluid, evaporation can affect the dynamics of colorimetric tests producing loss of color, non-uniform spot coverage, and/or undesired changes over time.

With reference toFIG. 2, this figure depicts a simplified diagram of a three dimensional (3D) microfluidic device200in accordance with an illustrative embodiment. In the embodiment, microfluidic device200is a multilayer device including an entry layer202, an analysis layer204, and an output layer206. Entry layer202includes a sample input portion208, analysis layer204includes a colorimetric chemical reagent portion210including one or more chemical reagents, and output layer includes colorimetric result portions212. In the illustrated embodiment, input portion208, colorimetric chemical reagent portion210, and colorimetric result portions212are formed of hydrophilic substrates (e.g., paper) constrained by hydrophobic material (e.g., a wax) deposited on the substrate.

During use of microfluidic device200, a fluid to be tested is applied to sample input portion208of entry layer202. The fluid flows to chemical reagent portion210of analysis layer204and reacts with the chemical reagents to produce one or more colorimetric results. The colorimetric results are viewable in colorimetric result portions212of output layer206.

With reference toFIG. 3, this figure depicts simplified processes300for fabricating a paper-based microfluidic device in accordance with illustrative embodiments. The embodiments ofFIG. 3illustrate a first process using wax printing to produce a microfluidic device, and a second alternative process using a stamping method to produce a microfluidic device. In the first process, a single patterned layer on a single sheet is produced from printing a predetermined pattern layout of wax or other hydrophobic material upon a target substrate302using a wax printing process304. In an embodiment, target substrate302is a paper substrate such as cellulose chromatography paper. Although various embodiments discussed herein are described as printing a wax material upon a substrate, it should be understood that in other embodiments any suitable hydrophobic material may be printed upon a substrate.

During a reflow process306, one or more printed sheets of substrate302are inserted into a thermal envelope (e.g., an isothermal envelope) between layers of thermally reflective material, and may be separated by sacrificial absorption paper sheets for protection. In particular embodiments, the thermal envelope includes laminated foil film covers with one or more internal wax absorption layers to create an isothermal environment or cavity for more uniform reflow heat distribution through the substrate thickness. The thermal envelope is inserted into a laminator device, and the laminator device applies heat and pressure to the thermal envelope and substrate to reflow the wax or other hydrophobic material. In particular embodiments, the laminator device may apply several passes at particular temperatures according to a laminator optimized recipe. A particular example of a laminator optimized recipe may include heating to approximately 150 degrees Celsius (C) and applying five passes for a one sided layer of substrate or eight passes for three sheets of a one-sided layer of substrate.

Alternatively, the thermal envelope may be inserted in a hot press instead of a laminator device to apply heat and pressure to the thermal envelope and substrate and a hot press optimized recipe is applied. A particular example of a hot press optimized recipe may include heating to approximately 200 degrees C. for 200 seconds for a single layer of substrate. The patterned sheets are then removed from the thermal envelope to produce a substrate with a patterned hydrophobic wax layout308.

One or more advantages that may be provided in one or more embodiments by the reflow process306using a thermal envelope such as reduced in-plane wax diffusion during reflow, reduced channel wall roughness, increased yield, reduced waste, or reduced wax leakage. Other advantages that may be provide in one or more embodiments include providing for simultaneous reflow of larger printed areas and the possibility of multiplexing of several sheets for increased throughput.

During an assembly process318, a customized mask is created and applied to substrate with a patterned hydrophobic wax layout308. In particular embodiments, the mask is constructed of a wooden, plastic, and/or metal material. In the embodiment the mask covers and protects hydrophilic portions of the substrate, and an adhesive spray is applied to the substrate. In the embodiment, the mask protects the hydrophilic portions from becoming hydrophobic due to contamination by the adhesive spray. The mask is then separated from substrate308and the process is repeated for each layer. The layers are stacked to form a layer stack320.

In a protective layer process322, a protective coating including hydrophobic material is applied over the output layer surface of the substrate to form a microfluidic device324. In one or more embodiments, the protective coating improves uniformity of colorimetric output and reduces evaporation effects by adding a hydrophobic protective layer about the colorimetric output. Various methods may be used to apply the protective coating according to one or more embodiments including, but not limited to: (1) applying a plastic cover via a lamination step (e.g., 110 degrees C. for 45 seconds per sheet using a laminator device); (2) parafilm protective layer adhesion through a heating step (e.g., 60 degrees C. for 10 seconds per sheet in a hot-press); (3) applying an adhesive transparent layer on one side via pressure; or (4) impermeabilizer spraying and drying in which no heat or pressure is required).

Still with reference toFIG. 3, the second alternative process using a stamping process314includes transferring a wax (or other hydrophobic) design from a printer to an intermediate surface, and then transferring the design from the intermediate surface to a substrate (e.g., paper) through a heating step that enables creating hydrophobic barriers within arbitrary types of substrates (e.g., varying thickness and/or varying porosity). During stamping process314, hydrophobic (e.g., wax) layouts are printed on transfer medium such as a plastic slide, metal plate, or metal cylinder). In the illustrated embodiments, a first transfer medium310and a second transfer medium312are used to transfer layouts to a substrate. The transfer surfaces of first transfer medium310and second transfer medium312are aligned with each other if a top and bottom layouts exit and aligned with the test substrate in a stacked arrangement. The stack is heated and pressure is applied resulting in the hydrophobic layout being transferred from the transfer medium surfaces into a thickness of the pattern hydrophobic layout316. In the illustrated embodiment, two patterned layers are produced on a single sheet of paper. Alternative embodiments may use the same geometric wax pattern on both sides of the paper substrate. In yet another embodiment, the stamping method may be used on a single side of the substrate only.

An advantage that may be provided by stamping process314in one or more embodiments includes that the process may be applicable to any substrate regardless of size, weight, thickness, etc. Another advantage that may be provided by stamping process314in one or more embodiments includes providing for the capability of multilayer wax deposition by resolving problems with alignment between both substrate sides which may be problematic for wax printers.

In the embodiment, in a similar manner as described with respect to the first process, assembly process318, a customized mask is created and applied to substrate with a patterned hydrophobic layout316. The mask is then separated from substrate and the process is repeated for each layer. The layers are stacked to form a layer stack320. In protective layer process322, the protective coating including hydrophobic material is applied over the output layer surface of the substrate to form a microfluidic device324.

With reference toFIG. 4, this figure depicts simplified processes400for fabricating a paper-based microfluidic device in accordance with other illustrative embodiments. The embodiments ofFIG. 4are similar to those described with respect toFIG. 3except that the protective hydrophobic layer can be applied before assembly in order to protect chemical reagents integrated into the substrate from high temperatures. The embodiments ofFIG. 4illustrate a first process using wax printing to produce a microfluidic device, and a second alternative process using a stamping method to produce a microfluidic device. In the first process, a single patterned layer on a single sheet is produced from printing a predetermined pattern layout of wax or other hydrophobic material upon a target substrate402using a wax printing process404.

During a reflow process406, one or more printed sheets of substrate402are inserted into a thermal envelope between layers of thermally reflective material, and may be separated by sacrificial absorption paper sheets for protection. The thermal envelope is inserted into a laminator device, and the laminator device applies heat and pressure to the thermal envelope and substrate to reflow the wax or other hydrophobic material. Alternatively, the thermal envelope may be inserted in a hot press instead of a laminator device to apply heat and pressure to the thermal envelope and substrate and a hot press optimized recipe is applied. The patterned sheets are then removed from the thermal envelope to produce a substrate with a patterned hydrophobic wax layout408.

In a protective layer process410, a protective coating including hydrophobic material is applied over the output layer surface of the substrate. During an assembly process420, a mask is created and applied to the substrate408. In the embodiment the mask covers and protects hydrophilic portions of the substrate, and an adhesive spray is applied to the substrate. In the embodiment, the mask protects the hydrophilic portions from becoming hydrophobic due to contamination by the adhesive spray. The mask is then separated from substrate408and the process is repeated for each layer. The layers are stacked to form a microfluidic device422.

Still with reference toFIG. 4, the second alternative process using a stamping process416includes transferring a wax (or other hydrophobic) design from a printer to an intermediate surface, and then transferring the design from the intermediate surface to a substrate (e.g., paper) through a heating step that enables creating hydrophobic barriers within arbitrary types of substrates (e.g., varying thickness and/or varying porosity). During stamping process416, hydrophobic (e.g., wax) layouts are printed on transfer medium such as a plastic slide, metal plate, or metal cylinder. In the illustrated embodiments, a first transfer medium412and a second transfer medium414is used to transfer layouts to a substrates. The transfer surfaces of first transfer medium412and second transfer medium414are aligned with each other if a top and bottom layouts exit and aligned with the test substrate in a stacked arrangement. The stack is heated and pressure is applied resulting in the hydrophobic layout being transferred from the transfer medium surfaces into a thickness of the pattern hydrophobic layout418. In the illustrated embodiment, two patterned layers are produced on a single sheet of paper. Alternative embodiments may use the same geometric wax pattern on both sides of the paper substrate. In yet another embodiment, the stamping method may be used on a single side of the substrate only.

In protective layer process410, a protective coating including hydrophobic material is applied over the output layer surface of substrate408. During assembly process420, a mask is created and applied to the substrate418. In the embodiment the mask covers and protects hydrophilic portions of the substrate, and an adhesive spray is applied to the substrate. In the embodiment, the mask protects the hydrophilic portions from becoming hydrophobic due to contamination by the adhesive spray. The mask is then separated from substrate418and the process is repeated for each layer. The layers are stacked to form microfluidic device422.

With reference toFIG. 5, this figure depicts a simplified stamping process500for depositing a hydrophobic pattern on a substrate during fabrication of a microfluidic device in accordance with an illustrative embodiment. In the embodiment, a transparent transfer surface502of a transfer medium is provided to a wax printer503. In the illustrated embodiment, the wax printer503prints a wax pattern layout504on one or more transfer mediums to produce a first transfer surface504A and a second transfer surface504B. In the embodiment, first transfer surface504A is aligned with a top surface of a substrate506, and second transfer surface504B is aligned with a bottom surface of substrate506. Further, first transfer surface504A and second transfer surface504B are aligned with one another to form a stack. In a particular embodiment, substrate506is a paper substrate.

In the embodiment, pressing and heating508is applied to the stack. In a particular embodiment, the stack is heated at approximately 150 degrees C. for one minute under pressure using a hot press. As a result, the wax pattern layout is transferred from first transfer surface504A and second transfer surface504B to the top and bottom surfaces, respectively, of substrate506to form wax patterned substrate510. Accordingly, a process is provided for transferring a wax or other hydrophobic material design from a printer to an intermediate surface, and from the intermediate surface to a substrate through heating to enable creating of hydrophobic barriers within arbitrary types of substrates of varying materials (e.g., paper fibers), varying thickness, or varying porosity. Further, a process is provided for creating 3D hydrophobic geometries by patterning both sides of a substrate with accurate alignment. In another illustrative embodiment, hydrophobic material design may be transferred to the intermediate surfaces by means alternative to wax printing such as stencil transfer.

With reference toFIG. 6, this figure depicts a flowchart of an example process600for fabricating a microfluidic device in accordance with an illustrative embodiment. In block602, a printing device of a fabrication system receives a target substrate. In a particular embodiment, the target substrate is a paper substrate. In block604, the printing device deposits a wax (or other hydrophobic material) pattern layout on the target substrate using a wax printing process. In block606, the target substrate with the wax pattern layout is inserted into a thermal envelope or other isothermal environment. In particular embodiments, the thermal envelope includes laminated foil film covers with one or more internal wax absorption layers to create an isothermal environment or cavity for more uniform reflow heat distribution through the substrate thickness.

In block608, the thermal envelope and substrate is inserted into a lamination device. In block610, heat and pressure is applied to the thermal envelope and substrate by the lamination device to reflow the wax pattern layout. In particular embodiments, the lamination device may apply several passes at particular temperatures according to a laminator optimized recipe. Alternatively, the thermal envelope may be inserted in a hot press instead of a lamination device to apply heat and pressure to the thermal envelope and substrate using hot press optimized recipe.

In block612, the target substrate is removed from the thermal envelope to produce a substrate with a patterned hydrophobic wax layout. In block614, the fabrication system determines whether the current layer is the last layer of the microfluidic device. If the current layer is not the last layer, in block616the fabrication system proceeds to the next layer and process600returns to block602.

If the current layer is the last layer, process600proceeds to block618. In block618, the fabrication applies a mask to mask hydrophilic portions of the target substrate. In block620, the fabrication system applies an adhesive to the substrate. In block622, the fabrication separates the mask from the substrate. In block624, the fabrication system determines whether the last layer of the microfluidic device has had adhesive applied. If the last layer has not had adhesive applied, in block626the fabrication system proceeds to the next layer and process600returns to block618.

If the last layer has had adhesive applied, in block628the layers of the microfluidic device are assembled in a layer stack. In block630, the fabrication system applies a protective layer including a hydrophobic material to an output layer of the substrate to form a microfluidic device. Process600then ends.

With reference toFIG. 7, this figure depicts a flowchart of another example process700for fabricating a microfluidic device in accordance with an illustrative embodiment. In block702, a fabrication system receives a transfer medium. In particular embodiments, the transfer medium is a transparent medium. In other particular embodiments, the transfer medium may include a plastic slide or sheet, a metal plate, or a metal cylinder. In block704, a printing device of the fabrication system prints a wax pattern layout or other hydrophobic material pattern layout on the transfer medium.

In block706, the fabrication system aligns the transfer medium with a target substrate to form a stack. In block708, the fabrication system applies heat and pressure to the stack to transfer the wax pattern layout to the target substrate. In a particular embodiment, the fabrication system uses a hot stamping process to transfer the wax pattern layout to the target substrate. In block710, the fabrication system removes the transfer medium.

In block712, the fabrication system determines whether the current layer is the last layer of the microfluidic device. If the current layer is not the last layer, in block714the fabrication system proceeds to the next layer and process700returns to block702.

If the current layer is the last layer, process700proceeds to block716. In block716, the fabrication applies a mask to mask hydrophilic portions of the target substrate. In block718, the fabrication system applies an adhesive to the substrate. In block720, the fabrication separates the mask from the substrate. In block722, the fabrication system determines whether the last layer of the microfluidic device has had adhesive applied. If the last layer has not had adhesive applied, in block724the fabrication system proceeds to the next layer and process700returns to block716.

If the last layer has had adhesive applied, in block726the layers of the microfluidic device are assembled in a layer stack. In block728, the fabrication system applies a protective layer including a hydrophobic material to an output layer of the substrate to form a microfluidic device. Process700then ends.

An advantage that may be provided by an embodiment is that 2D and 3D channel fabrication on arbitrary substrate types (e.g., paper, very thick substrates, or very porous substrates) are enabled by means of a novel “stamping” process. In an embodiment, the stamping process may also resolve issues with alignment when using a printing device on both sides of a substrate. Another advantage that may be provided by an embodiment is of improved fidelity and repeatability by means of a reflow process using a novel thermal envelope process for reduced reflow-induced wax diffusion. Another advantage that may be provided by an embodiment is the use of a thermal envelope may increase yield and throughput as well as reduce waste. Another advantage that may be provided by an embodiment is that the patterning processes are compatible with various heating techniques such as hot-press, lamination, or hot cylinders.

Another advantage that may be provided by an embodiment is that of increased yield can be achieved by the improved assembly process utilizing a custom spraying mask that prevents adhesive from reaching unwanted areas and rendering channels hydrophobic.

Another advantage that may be provided in an embodiment is that improved uniformity and coverage of colorimetric output regions or other output layer regions and longer result persistence by reducing evaporation effects via the addition of a hydrophobic protective coating. Another advantage that may be provided by an embodiment is that a protective coating may provide enhanced protection for reagents embedded in a substrate (e.g., a paper fiber matrix), thus provided longer shelf-life for the microfluidic device.