Enhancement and Quenching of Single-Molecule Fluorescence

TLDR

Local field enhancement boosts excitation while nonradiative energy transfer to a gold nanoparticle quenches quantum yield, producing competing effects that have yielded either fluorescence enhancement or quenching in prior experiments. The study investigates how a single molecule’s fluorescence rate varies with its distance to a laser‑irradiated gold nanoparticle. The authors combine experimental measurements with theoretical modeling to probe the distance‑dependent fluorescence rate of a single molecule near a laser‑irradiated gold nanoparticle. The experiments reveal a continuous transition from fluorescence enhancement to quenching as the molecule–particle distance changes, a behavior that cannot be captured by treating the particle as a polarizable sphere in the dipole approximation.

Abstract

We present an experimental and theoretical study of the fluorescence rate of a single molecule as a function of its distance to a laser-irradiated gold nanoparticle. The local field enhancement leads to an increased excitation rate whereas nonradiative energy transfer to the particle leads to a decrease of the quantum yield (quenching). Because of these competing effects, previous experiments showed either fluorescence enhancement or fluorescence quenching. By varying the distance between molecule and particle we show the first experimental measurement demonstrating the continuous transition from fluorescence enhancement to fluorescence quenching. This transition cannot be explained by treating the particle as a polarizable sphere in the dipole approximation.