title: Quantitative study of the gold-enhanced fluorescence of CdSe/ZnS nanocrystals as a function of distance using an AFM probe.
abstract: We report total internal reflection fluorescence microscopy (TIRFM) measurements using an atomic force microscope (AFM) probe to investigate the quantitative fluorescence profiles of CdSe/ZnS nanocrystals (NCs), which interact with gold surfaces, as a function of the gold-NC distance. First, a silica bead was glued to an AFM cantilever. CdSe/ZnS NCs were then immobilized on the silica-bead-functionalized AFM probe for control of the gold-NC distance, while a gold thin film served as the metal surface on a glass substrate. As a result of coexistent fluorescence resonance energy transfer and localized surface plasmon resonance (LSPR) coupling, a strong enhancement was observed at 15 nm, while fluorescence suppression was seen at a proximal distance. For further quantitative discussions of the effects of the metal surface on the fluorescence behavior of single NCs, we introduced a gold-deposited silica bead onto the AFM cantilever to regulate the gold-NC distance. Subsequently, the CdSe/ZnS NCs were immobilized on a glass surface. As a result of compensation for the contribution of photobrightening, the NC fluorescence profile for the glass surface also clearly displayed the LSPR-coupled enhancement at 10 nm. In contrast, it was discovered that positioning of the gold surface at a proximal single NC gave rise to quenching of the NC fluorescence. Our findings suggest that a method using an NC-functionalized AFM probe allows us to quantitatively investigate the NC fluorescence under the effects not only of a metal surface but also of an evanescence field.
authors.affiliation: Department of Electronic Chemistry, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa, 226-8503, Japan.
authors.forename: Sang Yun
authors.initials: SY
authors.lastname: Lee
authors.forename: Kouta
authors.initials: K
authors.lastname: Nakaya
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Hayashi
authors.forename: Masahiko
authors.initials: M
authors.lastname: Hara