Localized surface plasmon coupled fluorescence

Localized Surface Plasmon Coupled Fluorescence Fiber-optic Biosensor... 

Hsieh B.-Y., Chang Y.-F., Ng M.-Y., Liu W.-C., Lin C.-H., Wu H.-T., and Chou C. (2007). Localized surface plasmon coupled fluorescence fiber-optic biosensor with gold nanoparticles. Anal. Chem. 79, 3487-3493. 

Kreiter, M., Neumann, T., Mittler, S., Knoll, N., and Sambles, J. R. (2001). Fluorescent dyes as a probe for the localized field of coupled surface plasmon-related resonances Physical Review B 64. 

The electromagnetic nature of surface-enhanced Raman scattering (SERS) and plasmon-enhanced fluorescence (PEF) involves resonant excitations of localized plasmons (LPs) in the near-field of nanosized noble metal particles or films, coupling them with surrounding scatterers and detection of their secondary emission in the far field. Employment of these plasmonic phenomena are proposed, for example, as a new approach to increase brightness of heavily labeled macromolecules [1]. 

Earlier observations by Cesario et al. [60] of a decay in fluorescence for arrays of Au nanoparticles spaced above a Ag film by a Si02 layer of increasing thickness, were interpreted as due to the finite vertical extent of the evanescent fields associated with a surface plasmon. In this model the coupling results in an enhanced interaction between individual localized plasmons at individual nanostructures [61] and thus an enhancement in the radiative efficiency increasing the spacer layer thickness moves the nanowires out of the evanescent field of the surface plasmon. A possible physical mechanism for the experimentally observed decay involves nonradiative decay of the excited states. The aluminum oxide deposited in these experiments was likely to be nonstoichio-metric, and defects in the oxide could act as recombination centers. Thicker oxides would result in higher areal densities of defects, and decay in fluorescence. A definitive assignment of the mechanism for the observed fall off of fluorescence would require determination of the complex dielectric function of our oxides (as deposited onto an Ag film), and inclusion in the field-square calculations. Finally it should be noted that at very small thicknesses quenching of the fluorescence is expected [38,62] consistent with observations of an optimum nanowire-substrate spacer thickness. 

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