Abstract

Ideal bioimaging probes in fluorescence microscopy are bright, biocompatible, offer a large signal-to-noise ratio against autofluorescence, and can be specifically attached to target biomolecules of interest. Fluorescent proteins have been engineered towards this goal. However, a limitation of fluorescent proteins is the quantum yield; the low brightness of the probes limits the contrast between the structure of interest and the background. This limitation can be overcome using plasmonic enhancement by coupling the electronic resonances of the molecule to the plasmonic resonances of a metal nanoparticle with a dominant radiative broadening [1]. This allows an enhanced fluorescence emission of the molecule by increased absorption via near-field enhancement and increased radiative decay rate of the molecule by the Purcell effect, with photons emitted to the far field. Gold nanorods (GNRs) have a surface plasmon resonance which can be tuned by changing their aspect ratio to match the absorption and emission wavelengths of the fluorophore. Therefore, coupling GNRs to fluorescent proteins offers a route toward developing improved imaging probes. Moreover, understanding the photophysical properties of the fluorescent probe used is vital in their application. These properties can be probed at low temperatures where the coupling between the vibrations and electronic transitions is not masked by dominant homogenous broadening.

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