Fine-tuning the electrochemical deposition of Ag nanoparticles on TiO2 nanotube array films for Surface-Enhanced Raman Scattering

In this work, we report the controlled electrodeposition of Ag nanoparticles on anodic TiO2 nanotube films (TiO2-NTFs) for their application as Surface-Enhanced Raman Scattering (SERS) platforms. The influence of TiO2 crystallinity, AgNO3 precursor concentration, and the number of galvanostatic deposition cycles was systematically investigated to achieve fine control over nanoparticle size, surface density, and distribution. Morphological analysis revealed that amorphous and anatase TiO2-NTFs promoted uniform, high-density Ag nanoparticle deposition. In contrast, the mixed anatase–rutile film exhibited lower Ag nanoparticle coverage and cookie-type aggregates, which may be associated with its higher wall resistivity. At low AgNO3 concentrations, uniform and nanosized Ag particles were obtained, whereas higher concentrations led to localized nucleation and the formation of microcrystals. The resulting TiO2-NTF/Ag films displayed strong SERS activity toward 2-mercaptopyridine, with responses that, under some conditions, exceeded those reported for similar photoreduction-based platforms. Notably, the SERS performance depends on the balance among nanoparticle size, surface density, and spatial distribution, highlighting the importance of precise electrochemical control in tailoring high-performance SERS substrates.