Multicolor colorimetric assay for copper ion detection based on the etching of gold nanorods

An effective, selective, and multicolor colorimetric assay for Cu 2+ detection based on the regulation of peroxidase-like nanozyme-mediated etching of gold nanorods (Au NRs) is proposed. Cu 2+ -creatinine complex is selected as the nanozyme that exhibits excellent peroxidase-like activity even in the case of low concentration of Cu 2+ , which can catalyze 3,3,5,5-tetramethylbenzidine (TMB) to produce oxidized TMB (TMB + ) in the presence of hydrogen peroxide, and TMB + is oxidized to generate TMB 2+ after adding H + , and the TMB 2+ can etch Au NRs. The determination of Cu 2+ is achieved based on the blue shift of the longitudinal localized surface plasmon resonance peak of Au NRs. Under the optimal conditions, the developed colorimetric assay exhibits high sensitivity for the detection of Cu 2+ (limit of detection is 0.034 μM) with a wide linear range of 0.05–4.0 μM ( R 2  = 0.987). The solution shows a rainbow-like color in response to the increase of Cu 2+ concentration, which can realize the semi-quantitative detection of Cu 2+ by naked eyes. In addition, the developed method exhibits excellent selectivity for Cu 2+ -detection. The established method was used for the determination of Cu 2+ in lake water, soil, and normal human serum with satisfactory recovery of spiked samples. Graphical abstract