Distance-Based Detection of Ag+ with Gold Nanoparticles-Coated Microfluidic Paper

In this study, we developed a microfluidic paper analysis device (μPAD) for distance-based detection of Ag + in water. The μPAD was manufactured by wax printing method on filter paper. Then, a layer of gold nanoparticles (AuNPs) was deposited and ascorbic acid was printed on the channel. In the detection, Ag + was reduced by ascorbic acid and coated on the surface of the AuNPs on the channel, forming Au@Ag core/shell nanoparticles. Based on the capillary flow principle, different concentrations of Ag + formed different distances of color ribbons. Thus, quantitative detection of Ag + can be achieved by measuring the distance of the color ribbon. The detection limit of this method was as low as 1 mg·L −1 within 15 min and the interference of common metal ions in water can be eliminated. In conclusion, this method had successfully realized the leap from colorimetry to direct reading, realizing fast read and easy manipulation with low-cost.