Precipitation assay meets low wettability on paper: a simple approach for fabricating patterned paper sensors

The development of paper-based analytical platforms has brought a requirement on easily creating patterned paper sensors. This article describes a facile method of fabricating patterned paper sensors using a combination of wettability-controlled paper and the precipitation assays between analytes and sensing elements. Different from common fabrication processes in which patterned channels are defined by creating hydrophobic barriers, herein the direct deposition of the patterns of sensing elements onto paper is performed by simple writing and stamping. Without hydrophobic treatment, the patterned sensing components can remain in place on the paper substrate whose wettability is tuned via bovine serum albumin (BSA) modification. After exposure to the analytes, the precipitates of sensing reactions are not delocalized, giving a simple and successful patterned signal readout. The results of typical colorimetric assays show that slow capillary flow and insoluble products together on paper provide an extremely easy route for fabricating multifunctional patterned paper sensors.