Modification-free and N-acetyl-L-cysteine-induced colorimetric response of AuNPs: A mechanistic study and sensitive Hg2+ detection

• The proposed method could be easily performed without any pre-modification steps.
• A theoretical study was also used to illustrate the mechanism of this system.
• This colorimetric assay was simple, cost-effective, sensitive and selective.

A facile yet sensitive and selective method was proposed for Hg2+ detection based on N-acetyl-L-cysteine(NAC)-induced colorimetric response of AuNPs. The proposed method can be easily performed by introducing the premixing of NAC and Hg2+ into as-prepared citrate-capped AuNPs solution. A combination of experimental and theoretical studies was applied to illustrate the mechanism of this AuNPs colorimetric system. The strong interaction of NAC and AuNPs through Au–S bond could lead to the aggregation of AuNPs, but the formation of NAC-Hg-NAC complex decreased the affinity between NAC and AuNPs and resulted in an anti-aggregation effect. Therefore, the color of the AuNPs solution would progress from purple to red with the increase of Hg2+ concentration. The proposed method had a high sensitivity with a limit of detection of 9.9 nM. Coexistent metal ions, including Cd2+, Mn2+, Al3+, Ag+, K+, Mg2+, Ca2+, Cr3+, Cu2+, Fe3+, Pb2+, Ni2+ and Zn2+, did not interfere with the detection of Hg2+. This method can be used to monitor Hg2+ in tap water.

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