Au Nanoparticles (NPs) Decorated Co Doped ZnO Semiconductor (Co400-ZnO/Au) Nanocomposites for Novel SERS Substrates

Abstract

Au nanoparticles were decorated on the surface of Co-doped ZnO with a certain ratio of Co²⁺/Co³⁺ to obtain a novel semiconductor-metal composite. The optimal substrate, designated as Co₄₀₀-ZnO/Au, is beneficial to the promotion of separation efficiency of electron and hole in a semiconductor excited under visible laser exposure, which the enhances localized surface plasmon resonance (LSPR) of the Au nanoparticles. As an interesting finding, during Co doping, quantum dots of ZnO are generated, which strengthen the strong semiconductor metal interaction (SSSMI) effect. Eventually, the synergistic effect effectively advances the surface enhancement Raman scattering (SERS) performance of Co₄₀₀-ZnO/Au composite. The enhancement mechanism is addressed in-depth by morphologic characterization, UV-visible, X-ray diffraction, photoluminescence, X-ray photoelectron spectroscopy, density functional theory, and finite difference time domain (FDTD) simulations. By using Co₄₀₀-ZnO/Au, SERS detection of Rhodamine 6G presents a limit of detection (LOD) of 1 × 10⁻⁹ M. As a real application, the Co₄₀₀-ZnO/Au-based SERS method is utilized to inspect tyramine in beer and the detectable concentration of 1 × 10⁻⁸ M is achieved. In this work, the doping strategy is expected to realize a quantum effect, triggering a SSSMI effect for developing promising SERS substrates in future.