A distance-based paper analytical device: Visual quantification of salt in foods with silver nanoparticles on paper

Abstract

Using silver nanoparticles (AgNPs) and carboxymethyl cellulose (CMC), a simple distance-based paper analytical device (dPAD) was developed for the determination of chloride ions in food products. The determination of chloride ions was based on the Mohr argentometric method without the chromium compound. A hydrophobic barrier was created on chromatography paper using a wax-printing technique. The barrier protected a channel that was impregnated with AgNPs and CMC. In the presence of chloride, chloride ions moved along the channel, reacting with AgNPs, and forming an AgNPs-Cl sediment deposited as a white/gray precipitation in the orange-colored channel. The chloride ion concentration was interpreted from the length of the color change visualized with the naked eye without external equipment. The amount and volume of AgNPs and CMC impregnated on the chromatography paper were optimized. The response of the AgNPs-CMC/dPAD to the chloride ion was linear from 0.01 to 1.00 % w/v (r = 0.9931). In addition, the proposed device was stable for more than 28 days, with a relative response of 105 ± 3 % compared to day one, resulting in consistent and precise results. Intra-day (6 measurements) and inter-day (over 6 days) precision were excellent with RSDs less than 6 %. The developed dPAD was used to detect salt in twenty-five real samples, including instant noodles, condiments and sauces, and snacks. Recoveries ranged from 96 ± 5 to 105 ± 5 %. The proposed method showed acceptable accuracy, precision and good shelf life for monitoring chloride in food products at the point of need and demonstrated potential for commercial development.