UV-Irradiated and SPS-Constructed Vacancy-Rich Co-Doped TiO2 for Highly Sensitive SERS Detection via Enhanced Charge Transfer

Chemical enhancement in surface-enhanced Raman scattering (SERS) enables detection specificity by leveraging charge transfer (CT) between substrates and adsorbed molecules, a mechanism pivotal for designing next-generation SERS sensors with ultraselective molecular recognition capabilities. In this paper, based on the defect engineering, a Co-doped TiO₂ film was prepared by the sol-gel method and spark plasma sintering furnace (SPS) approach. Multimodal characterizations (X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), ultraviolet photoelectron spectrometry (UPS)) combined with the three-dimensional (3D) finite-difference time-domain (FDTD) simulation results reveal that Co doping enhances the Raman signal intensity via introducing oxygen vacancies and optimizes energy-level alignment. Innovatively, the charge transfer dynamics measured by ultrafast time-resolved photoluminescence spectroscopy (TRPL) further confirmed the superior carrier transfer property of the Co-doped TiO₂ films. Importantly, the coexistence of two charge transfer pathways were explored: direct charge transfer from Co_0.05Ti_0.95O₂ to R6G and charge transfer mediated by defect states generated through ultraviolet (UV) irradiation, which can significantly enhance the SERS sensitivity. The SERS substrate based on oxygen vacancy-engineered Co_0.05Ti_0.95O₂ demonstrates an excellent sensitivity and recycling performance. The EF of R6G adsorbed on optimized Co_0.05Ti_0.95O₂ with little Au is about 1.13 × 10⁸, and the LOD is about 7.9 × 10^-10 M with Rhodamine 6G (R6G) as the probe molecule. Furthermore, the highly ordered bowl-like Co_nTi_1-nO₂ arrays were prepared by photolithography, which exhibit superior stability, and the RSD of Rhodamine 6G (R6G) is about 3.6%.