Fluorescence near Metal Surfaces

Moving from discrete interactions between molecules to larger superstructures, Kuhn and coworkers used Langmuir-Blodgett techniques to construct surfaces modified by monolayers of D and A which were separated by non-fluores-cent spacer molecules in a multilayer sandwich arrangement [30]. The measured fluorescence intensity depended on the inverse fourth power of the separation between D and A, obeying the following  

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Lpiuo—i - ivr. It is clear in this case that a large fluorescence quenching occurs, and this is partly the origin of the common view that fluorescence near metal surfaces is always quenched. Even if FDMEF exists in such a case, its intensity would not be detectable. 

In 1979, Weber and Eagen" examined the decay channels responsible for the quenching of molecular fluorescence near metal surfaces. They showed that for a molecule located between 20 and 160 A from the surface, 80% of its lost energy will lead to surface plasmon excitation in the metal, while at much shorter distances, surface plasmon excitation will go to zero and electron-hole excitation will increase as a result. 

Sokolov K, Chumanov G, Cotton TM (1998) Enhancement of molecular fluorescence near the surface of colloidal metal films. Anal Chem 70 3898-3905... 

Johansson, P., Xu, H., and Kail, M. (2005). Surface-enhanced Raman scattering and fluorescence near metal nanoparticles. Phys. Rev. B 72 035427-1-17. 

Unified Treatment of Fluorescence and Raman Scattering Processes near Metal Surfaces. Physical Review Letters 93 243002/243001-243002/243004. 

Sokolov, K., Chumanov, G., and Cotton, T. M. (1998). Enhancement of Molecular Fluorescence near the Surface of Colloidal Metal Films. Anal Chem. 70 3898-3905. 

Figure 16.3 Modified Jablonski diagram ows the energy absorption effects of near metal surface enhanced fluorescence. The process involves o eating an excited electronic singlet state by optical absorption and subsequent emission of fluorescence with different decay paths.

Motivated by experiments on fluorescence quenching of dyes tethered on CNTs and studies on the decay of excited states near metal surfaces, we have studied the process of EET from fluorophores to a sheet of graphene. Starting from the Fermi... 

These effects are not limited to fluorophores excited by TIR, although TIR excitation is necessarily near a surface. The discussion in this section is of relevance to any mode of excitation of surface-proximal fluorescence. In many of the experiments involving fluorescence in cell biology, the fluorophores are located near a surface. Usually, this surface is an aqueous buffer/glass or plastic interface upon which cells grow. Occasionally, the interface may have a thin coating on it, such as a synthetic polymer, a metal, or a lipid bilayer. 

An increase in fluorescence quantum yield is possible due to the suppression of the nonradiative decay of fluorophores upon binding to metallic nanoparticles. However, radiative decay is dramatically increased near the surface of metal nanoparticles, whereas changes in knr are less sensitive to distance. 

Lakowicz, J. R., Malicka, J., D Auria, S., Gryczynski, I. (2003). Release of the self-quenching of fluorescence near silver metallic surfaces Anal. Biochem. 320 13-20. 

Gruhlke, R. W., Holland, W. R., and Hall, D. G. (1986). Surface-plasmon cross coupling in molecular fluorescence near a corrugated thin metal film. Phys. Revi. Lett. 30 2838-2841. 

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