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 (Cu 2+ ) based on anti-etching of gold nanorods (AuNRs) induced by cuprous ions (Cu + ). The formation of Cu + from the reaction between Cu 2+ 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 (H 2 O 2 ), resulting in a decrease in the amount of TMB 2+ product that can etch AuNRs, which is accompanied by the color changes from yellow to light orange. Thus, determination of Cu 2+ 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 Cu 2+ in solution can be achieved with naked eyes, and a dynamic range of 0 to 1.6 nM toward Cu 2+ was obtained. Graphical abstract Schematic representation of a colorimetric method for determination of Cu 2+ based on the anti-etching of gold nanorods induced by Cu + , which is from the reaction of Cu 2+ with sodium ascorbate.