TiO₂ multi-leg nanotubes for surface-enhanced Raman scattering

In the recent past, significant research efforts have been put forth to fabricate cost-effective substrates for surface-enhanced Raman scattering (SERS) applications. Here we propose semiconducting TiO 2 multi-leg nanotubes and Au nanoparticle-coated TiO 2 multi-leg nanotubes (TiO 2 MLNTs and Au/TiO 2 MLNTs) as SERS substrates. The unique multi-leg architecture of TiO 2 nanotubes demonstrated enhanced light-harvesting properties facilitated by an induced photonic absorption edge. Remarkable high SERS sensitivity is observed towards the detection of Methylene blue (MB), up to nM concentration (E.F. ∼10 4 ) using TiO 2 MLNTs. The same is attributed to the resonantly matched photonic absorption edge of TiO 2 MLNTs with the wavelength of incident laser probe light. On the other hand, the Au nanoparticle coating further leveraged the light absorption ability of TiO 2 MLNTs with the aid of localized surface plasmon resonance mode. As such, Au/TiO 2 MLNTs showed excellent enhancement in SERS sensitivity (E.F. ∼10 5 , for nM of MB) facilitated by the synergy between the plasmonic modes of Au and the photonic absorption mode of TiO 2 MLNTs. UV-Vis diffuse reflectance and Raman spectroscopy measurements are highlighted to elucidate the light absorption and SERS sensitivity of the TiO 2 and Au/TiO 2 MLNTs.