Colorimetric sensing of copper(II) based on catalytic etching of gold nanorods

In this work, a sensitive colorimetric method for determination of copper(II) in aqueous solution was developed based on catalytic etching of gold nanorods (GNRs). CTAB stabilized GNRs were etched slowly by dissolved oxygen along the axial direction in NH3-NH4Cl (0.8/0.1 M) solution. The etching was accelerated by the addition of Cu2+ with very low concentration, leading to a dramatic decrease of the GNRs in length but little in diameter. The etching caused the longitudinal surface plasmon resonance (LSPR) absorption to decrease sharply and shift to the short-wave direction, accompanied by a color change from blue to slight red. Potential effects of relevant experimental conditions, including concentrations of NH3 and S2O32-, and incubation temperature and time were evaluated for optimization of the method. The proposed method is sensitive (LOD = 2.7 nM) and selective (by at least 100-fold over other metal ions except for Mn2+ and Pb2+) with a linear range from 7 to 50 nM. Furthermore, the cost-effective method allows rapid and simple determination of the content of copper in shellfish samples.