title: Super-resolution mapping of reactive sites on titania-based nanoparticles with water-soluble fluorogenic probes.
abstract: 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 TiO(2) nanoparticles at the single-particle, single-molecule levels. The minimum probe concentration to detect single-product molecules on a single TiO(2) 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 TiO(2) 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.
authors.affiliation: The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan. tachi45@sanken.osaka-u.ac.jp
authors.forename: Takashi
authors.initials: T
authors.lastname: Tachikawa
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Yonezawa
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Majima
mesh_terms: D001665:Binding Sites; D008422:Materials Testing; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size; D012995:Solubility; D013050:Spectrometry, Fluorescence / Q000379:methods*; D014025:Titanium / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; C009495:titanium dioxide; D014025:Titanium