In situ plasmon-heating-induced generation of Au/TiO2 hot spots on colloidal crystals

Gold nanoparticles have been extensively investigated due their chemical and physical properties, which make them suitable for catalysis, optoelectronics and sensing. In particular, sensing and biodiagnostics take advantage of the affinity exhibited by gold nanoparticles towards thiols to form Au-(bio)-conjugates through a simple surface chemistry. Moreover, the chance to excite gold surface plasmons upon interaction with an electromagnetic field gave rise to ultra-sensitive diagnostic techniques such as surface plasmon resonance (SPR) and surface-enhanced vibrational spectroscopies (SEVSs). We report the in situ generation of Au/TiO2 micrometric spots on polymeric colloidal crystals. These spots resulted from the local crystallization of amorphous TiO2 (a-TiO2), which was induced by interaction between a low-power CW laser and closely aggregated gold nanoparticles, and promoted by the polymeric support. The enhancement of the electromagnetic field due to the presence of gold nanoparticles allowed the in situ SERS characterization of the anatase thin film. Finally, we showed that these spots can be used as model sites to investigate some reaction occurring at the metal oxide surface. This is an important benefit in some research fields, such as photocatalysis in nanoscaled devices, as it allows some parameters, like the thickness of the photocatalyst or the concentration of the catalytic substrate to be optimized. Moreover, these substrates could be conveniently employed as plasmonic photocatalysts, enabling a number of important reactions to occur with high efficiency and minimal light exposure. In perspective, this approach could easily be extended to other classes of compounds, opening new frontiers for plasmon heating-driven processes.