The mechanism of fluorescence enhancements of fiber-optic biosensor with metallic nanoparticles is studied using scattering theory of evanescent waves by a metallic nanoparticle in dilute solution approximation. High local-field enhancement in the vicinity of metallic nanoparticles resulting from localized surface plasmon excitation and the fluorescence enhancement is estimated by calculating averaged local-field enhancement and radiative-rate enhancement of fluorophores in the presence of metallic nanoparticles. The metallic nanoparticles not only provide strong local field to enhance the fluorescence signal of fluorophores, but also help to scatter the fluorescence signal and to increase the far-field detectable signals of the fiber-optic biosensor. The effects of the radius of gold nanoparticles, fluorophore-particle separation, and fiber-particle separation on the fluorescence enhancement are discussed in detail.
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