Plasmon‐Enhanced Two‐Photon Excitation Fluorescence and Biomedical Applications

Abstract

Localized surface plasmon resonance (LSPR) of metal nanoparticles (NPs) can modulate optical properties of nearby chromophores and metal NPs themselves. This chapter focuses on plasmon-enhanced two photon excitation fluorescence and its applications. It illustrates the photophysical processes involving excitation and fluorescence of a typical chromophore. Two-photon excitation fluorescence is expected to experience a similar enhancement–quenching transition as the NP–chromophore separation distance decreases. The chapter demonstrates Plasmon-enhanced one-photon excitation fluorescence in different systems. Metal-enhanced fluorescence was initially discovered on the film substrates and later demonstrated in the colloid solutions. Two-photon excitation fluorescence is expected to experience much larger enhancement than one-photon excitation fluorescence since two-photon excitation fluorescence is proportional to a higher order function of local electric field. Similar to the plasmon-enhanced two-photon excitation fluorescence of organic chromophores, separation distance between upconversion NPs (UCNPs) UCNP and metal NP are critical for enhancing the photoluminescence of UCNP.