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Super-Resolution Mapping of Reactive Sites on Titania-Based Nanoparticles with Water-Soluble Fluorogenic Probes

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journal contribution
posted on 22.01.2013, 00:00 by Takashi Tachikawa, Tomoyuki Yonezawa, Tetsuro Majima
Interfacial charge transfer at the heterogeneous surface of semiconductor nanoparticles is a fundamental process that is relevant to many important applications, such as photocatalysis, solar cells, and sensors. In this study, we developed new water-soluble fluorogenic probes for interfacial electron transfer reactions on semiconductor nanoparticles. The synthesized boron-dipyrromethene-based fluorescence dyes have one or two sulfonate groups, which confer solubility in aqueous media, and a dinitrophenyl group as a redox reaction site. These probes produce the corresponding fluorescent products via multiple interfacial electron transfer processes, allowing us to investigate the photoinduced redox reactions over individual pristine and Au-nanoparticle-deposited TiO2 nanoparticles at the single-particle, single-molecule levels. The minimum probe concentration to detect single-product molecules on a single TiO2 nanoparticle was found to be in the nanomolar range (<10 nM) in acidic solution. Furthermore, super-resolution mapping of the reaction sites revealed that visible-light-induced reduction reactions preferentially occurred on the TiO2 surface within a distance of a few tens of nanometers around the deposited Au nanoparticles. This result was qualitatively interpreted on the basis of plasmon-induced electron and/or energy transfer mechanisms. Overall, this study provides a great deal of valuable information related to solar-energy-conversion processes that is impossible or difficult to obtain from ensemble-averaged experiments.