FLASH: a rapid method for prototyping paper-based microfluidic devices

Abstract

This article describes FLASH (Fast Lithographic Activation of Sheets), a rapid method for laboratory prototyping of microfluidic devices in paper. Paper-based microfluidic devices are emerging as a new technology for applications in diagnostics for the developing world, where low cost and simplicity are essential. FLASH is based on photolithography, but requires only a UV lamp and a hotplate; no clean-room or special facilities are required (FLASH patterning can even be performed in sunlight if a UV lamp and hotplate are unavailable). The method provides channels in paper with dimensions as small as 200 microm in width and 70 microm in height; the height is defined by the thickness of the paper. Photomasks for patterning paper-based microfluidic devices can be printed using an ink-jet printer or photocopier, or drawn by hand using a waterproof black pen. FLASH provides a straightforward method for prototyping paper-based microfluidic devices in regions where the technological support for conventional photolithography is not available.

Fig. 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 (the paper is 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.

Fig. 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 in water 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.

Fig. 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. A μPAD patterned using sunlight (D). A μPAD from Technicloth (E), or a paper towel (F). The devices were filled with an aqueous blue dye (1 mM Erioglaucine).