A simple colorimetric sensor based on anti-aggregation of gold nanoparticles for Hg2+ detection

Abstract A new method has been proposed to realize the visual detection of Hg 2+ via anti-aggregation of gold nanoparticles (Au NPs). The positively charged Au NPs were prepared using poly(diallyldimethylammonium) chloride (PDDA) as reducer and stabilizer. In the presence of cysteine, the color of Au NPs solution turned from ruby red to royal purple, indicating the aggregation of Au NPs. Owing to the high stability constant of cysteine with Hg 2+ , the pre-incubation of Hg 2+ with cysteine would form Hg 2+ –cysteine complexes and significantly reduce the concentration of free cysteine molecules, thus the aggregation of Au NPs was interrupted since there was not enough inducer. With the increase of Hg 2+ concentration, the color of the Au NPs solution would progress from purple to red, allowing the visual detection of Hg 2+ ranging from 5.0 × 10 −8 to 1.0 × 10 −5  M, with a detection limit of 2.5 × 10 −8 M. The proposed method is convenient, low-cost and free of complex equipment, making it possible to analyze Hg 2+ in drinking water, rain water or water extracted air samples.