Enhanced SERS Detection Using TiO₂ Photonic Crystals with In-Situ-Grown Au/Ag Nanoparticles

Surface-enhanced Raman spectroscopy (SERS) has been widely utilized for the detection of disease biomarkers, pesticides, and environmental pollutants due to its exceptional sensitivity, real-time responsiveness, and unique interactions between adsorbates and substrates. Here, we present a composite metal/semiconductor material comprising TiO 2 nanosphere substrates integrated with in-situ-grown Au or Ag nanoparticles (NMNPs@TiO 2 ). These composite nanospheres are assembled by an electrophoretic self-assembly process to form a photonic crystal structure with three-dimensionally ordered periodic geometric features and show remarkable sensitivity and stability for SERS detection, achieving a detection limit as low as 10 –9 M for Rhodamine 6G. Beyond merely enhancing SERS signals by generating uniformly distributed metal plasmonic “hot spots” on TiO 2 substrates, similar to traditional semiconductor substrates, this photonic crystal substrate also exhibits advanced light absorption and localization capabilities. The absorbed light drives the defect excitation of TiO 2, facilitated by its multicrystalline structure. Excited electrons from the TiO 2 nanospheres contribute to the enhancement of localized surface plasmon resonance through charge transfer to noble-metal nanoparticles. Additionally, the synthesis of NMNPs@TiO 2 nanospheres avoids the use of toxic reagents, and substrate assembly is achieved through a simple electrodeposition process. This approach simplifies fabrication while enabling the production of SERS detectors with exceptional spatial and temporal signal stability. With increasing demands for higher detection sensitivity, signal uniformity, and detector durability for SERS detection applications, the NMNPs@TiO 2 nanosphere-based photonic crystal substrate underscores its potential to significantly improve the SERS detection efficiency, making it ideal for ultrasensitive chemical detection applications.