See Gold nanoparticles

Gold nanoparticles are virtually not luminescent, but silver nanoparticles show plasmon emissions with reasonable quantum yields. Furthermore, the non-radiative decay, resulting in electron-hole pair generation, may be used for photosensitization of wide bandgap semiconductors (see Figure 7.5) [16,17]. Similar effects may also be observed as direct photoinduced electron transfer between metal surfaces and surface-bound molecules [18]. 

Brust, M. Walker, M. Bethel , D, Schiffrin, D. J, Whyman, R. Synthesis of Ttiol-Derivatised Gold Nanoparticles in a Two-Phase Liquid-Liquid System, J. Chem. See., Chem. Commun. 1994. 801-802,... 

Kiihn, S., Hakanson, U., Rogobete, L., and Sandoghdar, V. (2006). Enhancement of ingle-Molecule Fluorescence Using a Gold Nanoparticle as an Optical Nanoantenna. Phys. Rev. Lett. 97 017402-1-4 see also Supplementary info. 

The Novotny group have performed confocal measurements of the fluorescoiee of single molecules at defined distances from 80 nm silver and gold nanoparticles [19, 23]. The sample is illuminated with a laser and the eonfocal measurements taken with an optical fibre tip with a gold nanoparticle placed at the tip, see Figure 11.3. The fluorophore molecules are well-dispersed on a cover-slip below the tip and so the nanoparticle-fluorophore distance is controlled by vertical movement of the optical fibre. 

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