The preparation of high-index facet Au/Cu NRs and their application for colorimetric determination ascorbic acid

Creating high-index facet gold nanorods (Au NRs) is important for catalytic application. The high-index facet exhibits tremendously catalytic activity comparing with low-index facet. Herein, Cu2+ ions were chosen to induce Au NRs to form high-index {200} facet. Firstly, Au/Cu NRs with high-index facets induce high-density charge distribution at local position, which led to the surface enhanced Raman scattering enhancement. Furthermore, the active electrons transfer from Au/Cu NRs to H2O2 make them show peroxidase-like properties. The catalytic activity of Au/Cu NRs was confirmed by the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidized TMB (oxTMB) by H2O2. According to Michaelis-Menten equation, the catalytic activity of Au/Cu was higher than Au NRs by 4.5 times. Meanwhile, the oxTMB molecules may be deoxidized to TMB molecules by the antioxidant of ascorbic acids. On the basis of this phenomenon, the colorimetric determination of ascorbic acid in real samples (vitamin drink) was developed with a detection limit of 25 mu M.