Tuning plasmon absorption of unmodified silver nanoplates for sensitive and selective detection of copper ions by introduction of ascorbate

Silver nanoplates as novel optical sensors for Cu²⁺ detection have been demonstrated. Silver nanoplates are synthesized via previous H₂O₂-NaBH₄ cyclic oxidation-reduction reactions. With introduction of ascorbate as mild reductants, Cu²⁺ ions are reduced into Cu⁺ and the Cu⁺ is further reduced to Cu, which is deposited on the surface of the silver nanoplates. The deposition of the Cu on the surface of the silver nanoplates allows a significant red-shift of their plasmon absorption. Therefore, trace Cu²⁺ can be detected. The shift of the plasmon absorption wavelength of silver nanoplates is proportional to the Cu²⁺ concentration over a range of 40-340 μmol L^-1 with a limit of detection of 9.0 μmol L^-1. Moreover, such silver nanoplate-based optical sensors provide good selectivity for Cu²⁺ detection, and most other metal ions do not disturb its detection. Moreover, the practicality of the proposed sensor was tested. This Cu²⁺ assay is advantageous in its simplicity, selectivity, and cost-effectiveness.