Label-free colorimetric sensing of copper(ii) ions based on accelerating decomposition of H2O2 using gold nanorods as an indicator

Abstract

A novel label-free colorimetric strategy was reported for sensitive detection of copper ions (Cu²⁺) by using the decelerating etching of gold nanorods (GNRs). H₂O₂ was employed as the oxidant for corrosion of GNRs, leading to the decrease of the aspect ratio of GNRs. In the absence of Cu²⁺, the redox corrosion of GNRs by H₂O₂ occurred rapidly, causing the distinct color change of GNRs from bluish green to purplish red. By virtue of the strong and specific catalysis by Cu²⁺ of the decomposition of H₂O₂, the rate of redox corrosion can be decelerated. Relevant experimental parameters, including pH value, concentrations of NaSCN and H₂O₂, incubation temperature and time were evaluated. Under optimal conditions, our method gave a good linear range of 10–300 nM (R = 0.9985) for Cu²⁺ and the detection limit with the naked eye is as low as 10 nM. Thus, the proposed colorimetric sensor is simple, sensitive (4.96 nM) and selective, and it has been successfully applied to detect Cu²⁺ in shellfish samples. Moreover, the potential mechanism was also discussed.