In Situ Observation of Enhanced Photoinduced Charge Separation in a Gold Nanoparticle Assembly Immobilized on TiO 2

Photoinduced charge separation on a hybrid titanium dioxide (TiO 2 ) 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 TiO 2 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 (λ=240‐300 nm). In contrast, the AuNP assembly on the TiO 2 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 TiO 2 surface contributes to efficient storage of the negative charge generated by excited electrons in TiO 2 during photoinduced charge separation.