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

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 TiO 2 ink synthesized through a simple flame thermal-assisted method is demonstrated. The resultant TiO 2 microspherical arrays (MSAs) exhibit extraordinary SERS sensitivity with an enhancement factor of 3.28 × 10 7 , 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 TiO 2 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 Hg 2+ 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.