A Preliminary Study on the Selective Detection of Hypochlorite Based on Antiagregation of AuNPs

Abstract

A preliminary study on the selective detection of hypochlorite using gold nanoparticles (AuNPs) has been carried out. Gold nanoparticles have been synthesized using sodium citrate as capping and stabilizing agent simultaneously at room temperature with no stirring and pH adjustment. Development of hypochlorite detection methods is based on the ability of hypochlorite to oxidize L-cysteine that can aggregate AuNPs through the formation of S‒Au bonds. The aggregated gold nanoparticles will change color from red for the original AuNPS to blue for the aggregated AuNPs. The presence of hypochlorite added to L-cysteine will oxidize the thiol group of L-cysteine thereby reducing the ability of L-cysteine to aggregate AuNPs. The higher the concentration of hypochlorite in L-cysteine, the more thiol groups are oxidized. Thus the presence of hypochlorite will act as anti-aggregation of L-cysteine-induced aggregation of AuNPs and therefore the color of solution is turned back to red from blue. This color change can be easily visualized by naked eye within 7 min. The existence of AuNPs, L-cysteine aggregated AuNPs, and AuNPs that have been used to detect hypochlorite have been seen using UV-Vis spectrophotometers and Transmission electron microscopy (TEM).