Visual assay for determination of copper ions based on anti-etching of gold nanorods induced by cuprous ions

The authors describe a colorimetric method for the determination of copper ions (Cu²⁺) based on anti-etching of gold nanorods (AuNRs) induced by cuprous ions (Cu⁺). The formation of Cu⁺ from the reaction between Cu²⁺ and sodium ascorbate causes the deactivation of the horseradish peroxidase (HRP), which is used as the catalyst for the reaction of 3,3',5,5'-Tetramethylbenzidine (TMB) and hydrogen peroxide (H₂O₂), resulting in a decrease in the amount of TMB²⁺ product that can etch AuNRs, which is accompanied by the color changes from yellow to light orange. Thus, determination of Cu²⁺ is achieved on the basis of AuNR absorbance at 450 nm. A determination limit as low as 0.28 nM at the 3S_blank level, and the detection of 0.4 nM Cu²⁺ in solution can be achieved with naked eyes, and a dynamic range of 0 to 1.6 nM toward Cu²⁺ was obtained. Graphical abstractSchematic representation of a colorimetric method for determination of Cu²⁺ based on the anti-etching of gold nanorods induced by Cu⁺, which is from the reaction of Cu²⁺ with sodium ascorbate.