Macroscale TiO₂ Microspherical Arrays with Multiple Synergistic Effect for Highly Sensitive Surface‐Enhanced Raman Scattering

Abstract Semiconductor materials represent an ideal choice for designing surface‐enhanced Raman scattering (SERS)‐based sensors due to their superior thermal and chemical stability compared to conventional metal materials. However, current SERS‐active semiconductor substrates have limitations such as low detection sensitivity and often complicated preparation steps, which restrict their real‐life applications. In this work, for the first time the feasibility of large‐area fabricating SERS‐active semiconductor substrates based on screen‐printing of micron‐sized TiO₂ ink synthesized through a simple flame thermal‐assisted method is demonstrated. The resultant TiO₂ microspherical arrays (MSAs) exhibit extraordinary SERS sensitivity with an enhancement factor of 3.28 × 10⁷, which represents one of the highest sensitivity and are the easiest strategy among the reported SERS‐active semiconductor substrates. Both experiments and simulations rationalize the observed enhancement factor and propose that multiple synergistic resonances, including Mie resonance, charge‐transfer resonance, and molecular resonance significantly boost the performance of semiconductor substrates. Dye‐modified TiO₂ MSAs are further exploited as the sensing platform for the development of a ratiometric SERS sensor, enabling the highly sensitive, selective, low cost, and stable detection of Hg²⁺ ions. This study opens up new possibilities for preparing a large‐scale SERS‐active semiconductor array, ultimately advancing the fields of semiconductor‐based SERS sensing technology.