In Situ Observation of Enhanced Photoinduced Charge Separation in a Gold Nanoparticle Assembly Immobilized on TiO2

Photoinduced charge separation on a hybrid titanium dioxide (TiO2) surface with a gold nanoparticle (AuNP) assembly immobilized via a biotin-streptavidin interaction was visualized by Kelvin force microscopy (KFM). Biotinylated AuNP (Biot-AuNP) with a diameter of ca. 15 nm was assembled using streptavidin (STV) and the AuNP assembly was immobilized on a TiO2 surface modified with 1-(3-aminopropyl)silatrane. KFM reveals that the local contact potential difference (CPD) of dispersed AuNP, which is -17 +/- 4.2 mV in the dark, undergoes a negative shift of -46 +/- 3.0 mV upon UV-irradiation (lambda=240-300 nm). In contrast, the AuNP assembly on the TiO2 surface exhibits a greater negative shift of -58 +/- 6.0 mV of the CPD, although the CPD value of -16 +/- 5.8 mV in the dark is similar to that of the dispersed AuNP. KFM visualization demonstrates that assembly of the AuNP on the TiO2 surface contributes to efficient storage of the negative charge generated by excited electrons in TiO2 during photoinduced charge separation.