Glutathione Functionalized Gold Nanoparticles for Colorimetric Detection of Didecyldimethylammonium Chloride

A facile, sensitive, and selective colorimetric detection method for the disinfectant, didecyldimethylammonium chloride (DDAC) in aqueous samples was developed using glutathione (GSH)-functionalized gold nanoparticles (GSH-AuNPs). DDAC shorten the interparticle distance and immediately aggregate the GSH-AuNPs, leading to a dynamic change from a wine-red to a dark purple color. Therefore, the DDAC concentration in environmental samples is detected quantitatively using the GSH-AuNP sensor by the naked eye or by UV-vis spectrophotometry. The amide carbonyl groups of GSH in this sensor coordinate to the positive ammonium ion center of DDAC and also participate in cross-linking. Moreover, the sensitivity of detection was improved and stabilized by adjusting pH and salt concentration, yielding 9.6-times higher sensitivity and a faster color change in the optimized GSH-AuNP system. The ratios of absorptions at 662 nm and 520 nm (A(662)/A(520)) of the modified AuNP solution exhibited a linear correlation with DDAC concentrations with a 1.2-ppm detection limit. The GSH-AuNPs bound to DDAC showed excellent selectivity compared to other quaternary ammonium compounds and metal cations. This cost-effective and selective sensing system allows for the rapid and facile determination of DDAC concentrations in aqueous samples.