Surface double defects-dominated TiO2 with high liquid phase stability for smart SERS sensing of dye additives in foods

Surface defect engineering is an effective strategy to regulate the physical and chemical properties of semiconductors for a wide range of applications. Herein, a surface-highly-reduced anatase TiO₂ (R-TiO₂) with double defects (surface oxygen vacancy defect and Ti³⁺ energy level defect) was developed as a plasmon-free surface-enhanced Raman scattering (SERS) substrate for ultrasensitive detection of food additives. Abundant surface oxygen vacancies enable R-TiO₂ to exist stably in liquid phase, which realizes a smart SERS detection for dye target molecules due to evading fluorescent interference from analytes, while SERS enhancement of analytes cannot be observed on the solid phase substrate at all. Due to the joint contribution of surface double defects, a multi-channel charge transfer mode and a stronger Herzberg-Teller coupling between substrate and analyte are formed, which greatly enhance SERS effect of the substrate for sensitive detection of dye additives in foods with an enhancement factor of 1.6 × 10⁶.