Inkjet-printed microfluidic multianalyte chemical sensing paper

This paper presents an inkjet printing method for the fabrication of entire microfluidic multianalyte chemical sensing devices made from paper suitable for quantitative analysis, requiring only a single printing apparatus. An inkjet printing device is used for the fabrication of three-dimensional hydrophilic microfluidic patterns (550-μm-wide flow channels) and sensing areas (1.5 mm x 1.5 mm squares) on filter paper, by inkjet etching, and thereby locally dissolving a hydrophobic poly(styrene) layer obtained by soaking of the filter paper in a 1 wt % solution of poly(styrene) in toluene. In a second step, the same inkjet printing device is used to print "chemical sensing inks", comprising the necessary reagents for colorimetric analytical assays, into well-defined areas of the patterned microfluidic paper devices. The arrangement of the patterns, printed inks, and sensing areas was optimized to obtain homogeneous color responses. The results are "all-inkjet-printed" chemical sensing devices for the simultaneous determination of pH, total protein, and glucose in clinically relevant concentration ranges for urine analysis (0.46-46 μM for human serum albumin, 2.8-28.0 mM for glucose, and pH 5-9). Quantitative data are obtained by digital color analysis in the L*a*b* color space by means of a color scanner and a simple computer program.