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.
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"The use of paper is growing step-by-step, finding analytical applications by the production and assembling of optical and electrochemical analytical devices: Whiteside's group  and others  reported interesting paper-based sensing platforms. Plasma oxidation , inkjet-printing , and photolithography  allow to pattern the paper forming " cellulosic channels " through the establishment of hydrophobic/hydrophilic areas where reagents and analytes can easily diffuse/react/purge before reaching the detector. Solid-ink printing, better known as wax printing, is a helpful and costeffective alternative in the paper patterning , and has been efficiently employed to fabricate microfluidic paper-based analytical devices (mPADs), mainly coupled to a colorimetric detection . "
[Show abstract][Hide abstract]ABSTRACT: Herein we describe a novel reagentless paper-based electrochemical phosphate sensor, manufactured with a simple and inexpensive approach. By following three easy steps, consisting of wax patterning, paper chemical modification, and electrode screen-printing, the filter paper provides an effective electroanalytical platform to sense phosphate ions in standard solutions and real samples (river water). The electrochemical properties of the paper-based platform were evaluated, firstly, by using ferricyanide as a redox mediator, proving no analyte-entrapment due to the cellulose lattice. Then, the reference colorimetric method for phosphate ions, which is based on the formation of phosphomolybdic complex, was successfully adapted to a reagentless electrochemically paper-based platform. This novel and highly sustainable configuration readily allows for the determination of phosphate ions with high reproducibility and long storage stability, achieving a detection limit of 4 μM over a wide linear range up to 300 μM. This in-house approach would be able to generically develop an affordable in situ and user-friendly sensing device without the addition of any reagent, to be applied for a broad range of analytes.
Full-text · Article · Mar 2016 · Analytica chimica acta
"PADs can be produced through photolithography, handcrafting, cutting, or printing methods. Photolithography methods  require a UV lamp, hotplate, and a mask, and embed the photoresist into the paper by means of UV exposure through the mask. In handcrafted methods, the devices are fabricated via a manual wax drawing or stamping process . "
[Show abstract][Hide abstract]ABSTRACT: General biochemistry detection on paper-based microanalytical devices (PADs) uses pipette titration. However, such an approach is extremely time-consuming for large-scale detection processes. Furthermore, while automated methods are available for increasing the efficiency of large-scale PAD production, the related equipment is very expensive. Accordingly, this study proposes a low-cost method for PAD manufacture, in which the reagent is applied using a modified inkjet printer. The optimal reaction times for the detection of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) are shown to be 6 and 7 min, respectively, given AST and ALT concentrations in the range of 5.4 to 91.2 U/L (R2 = 0.9932) and 5.38 to 86.1 U/L (R2 = 0.9944). The experimental results obtained using the proposed PADs for the concentration detection of AST and ALT in real human blood serum samples are found to be in good agreement with those obtained using a traditional spectrophotometric detection method by National Cheng Kung University hospital.
"In addition, paper is thin, available in a variety of thicknesses, is lightweight, easy to stack, store, and transport, is compatible with biological samples given its composition, and is available in many forms with a diverse range of properties . Since the seminal work of Martinez [6,89101112131415 a myriad of techniques to pattern paper have been detailed including laser [16,17], wax891018192021, and inject printing , plasma etching [23,24], cutting , and mechanical plotting . While there have been a number of reports detailing versatile and inexpensive fabrication methods for POC devices, there is an ever-increasing need in resource-limited areas for accessing quality diagnostic testing272829303132. "
[Show abstract][Hide abstract]ABSTRACT: In this communication, we describe microfluidic paper analytical devices (μPADs) easily fabricated from commercially available Sharpie ink permanent markers on chromatography paper to colorimetrically detect glucose using glucose oxidase (GOx). Here, solutions of horseradish peroxidase (HRP), GOx, and potassium iodide (KI)were directly spotted onto the center of the μPAD and flowed into samples of glucose that were separately spotted on the μPAD. Using an XY plotter (Roland DGA Corporation, Irvine, CA USA), several ink marks drawn in the paper act as the hydrophobic barriers, thereby, defining the hydrophilic fluid flow paths of the solutions. Two paper devices are described that act as independent assay zones. The glucose assay is based on the enzymatic oxidation of iodide to iodine whereby a color change from clear to brownish-yellow is associated with the presence of glucose. In these experiments, two designs are highlighted that consist of circular paper test regions fabricated for colorimetric and subsequent quantification detection of glucose. The use of permanent markers for paper patterning is inexpensive and rapid and does not require special laboratory equipment or technical skill.