Femtosecond Spectroscopy of Au Hot-Electron Injection into TiO₂: Evidence for Au/TiO₂ Plasmon Photocatalysis by Bactericidal Au Ions and Related Phenomena.

In the present work, we provide evidence for visible light irradiation of the Au/TiO₂ nanoparticles' surface plasmon resonance band (SPR) leading to electron injection from the Au nanoparticles to the conduction band of TiO₂. The Au/TiO₂ SPR band is shown to greatly enhance the light absorption of TiO₂ in the visible region. Evidence is presented for the light absorption by the Au/TiO₂ plasmon bands leading to the dissolution of Au nanoparticles. This dissolution occurs concomitantly with the injection of the hot electrons generated by the Au plasmon into the conduction band of TiO₂. The electron injection from the Au nanoparticles into TiO₂ was followed by femtosecond spectroscopy. The formation of Au ions was further confirmed by the spectral shift of the transient absorption spectra of Au/TiO₂. The spectral changes of the SPR band of Au/TiO₂ nanoparticles induced by visible light were detected by spectrophotometer, and the morphological transformation of Au/TiO₂ was revealed by electron microscopy techniques as well. Subsequently, the fate of the Au ions was sorted out during the growth and biofilm formation for some selected Gram-negative bacteria. This study compares the bactericidal mechanism of Au ions and Ag ions, which were found to be substantially different depending on the selected cell used as a probe.