Single‐Nanoparticle Photoelectrochemistry at a Nanoparticulate TiO2‐Filmed Ultramicroelectrode

Abstract An ultrasensitive photoelectrochemical method for achieving real‐time detection of single nanoparticle collision events is presented. Using a micrometer‐thick nanoparticulate TiO 2 ‐filmed Au ultra‐microelectrode (TiO 2 @Au UME), a sub‐millisecond photocurrent transient was observed for an individual N719‐tagged TiO 2 (N719@TiO 2 ) 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 2 film. The combination of theoretical simulation and high‐resolution photocurrent measurement allow electron‐transfer information of a single N719@TiO 2 nanoparticle to be quantified at single‐molecule accuracy and the electron diffusivity and the electron‐collection efficiency of TiO 2 @Au UME to be estimated. This method provides a test for studies of photoinduced electron transfer at the single‐nanoparticle level.