T-shirt ink for one-step screen-printing of hydrophobic barriers for 2D-and 3D-microfluidic paper-based analytical devices

This work presents the use of polyvinyl chloride (PVC) fabric ink, commonly employed for screening t-shirts, as new and versatile material for printing hydrophobic barrier on paper substrate for microfluidic paper-based analytical devices (mu PADs). Low-cost, screen-printing apparatus (e.g., screen mesh, squeegee, and printing table) and materials (e.g. PVC ink and solvent) were employed to print the PVC ink solution onto Whatman filter paper No. 4. This provides a one-step strategy to print flow barriers without the need of further processing except evaporation for 3-5 min in a fume hood to remove the solvent. The production of the single layer mu PADs is reasonably high with up to 77 devices per screening with 100% success rate. This method produces very narrow fluidic channel 486 +/- 14 gm in width and hydrophobic barrier of 642 +/- 25 mu m thickness. Reproducibility of the production of fluidic channels and zones is satisfactory with RSDs of 2.9% (for 486-mu m channel, n = 10), 3.7% (for 2-mm channel, n = 50) and 1.5% (for 6-mm diameter circular zone, n = 80). A design of a 2D-pPAD produced by this method was employed for the colorimetric dual-measurements of thiocyanate and nitrite in saliva. A 3D-mu PADs with multiple layers of ink-screened paper was designed and constructed to demonstrate the method's versatility. These 3D-mu PADs were designed for gas-liquid separation with in-situ colorimetric detection of ethanol vapor on the mu PADs. The 3D-mu PADs were applied for direct quantification of ethanol in beverages and highly colored pharmaceutical products. The printed barrier was resistant up to 8% (v/v) ethanol without liquid creeping out of the barrier.