Single-Nanoparticle Photoelectrochemistry at a Nanoparticulate TiO -Filmed Ultramicroelectrode.

An ultrasensitive photoelectrochemical method for achieving real-time detection of single nanoparticle collision events is presented. Using a micrometer-thick nanoparticulate TiO -filmed Au ultra-microelectrode (TiO @Au UME), a sub-millisecond photocurrent transient was observed for an individual N719-tagged TiO (N719@TiO ) nanoparticle and is due to the instantaneous collision process. Owing to a trap-limited electron diffusion process as the rate-limiting step, a random three-dimensional diffusion model was developed to simulate electron transport dynamics in TiO film. The combination of theoretical simulation and high-resolution photocurrent measurement allow electron-transfer information of a single N719@TiO nanoparticle to be quantified at single-molecule accuracy and the electron diffusivity and the electron-collection efficiency of TiO @Au UME to be estimated. This method provides a test for studies of photoinduced electron transfer at the single-nanoparticle level.