Plasmon-Enhanced Brightness and Photostability from Single Fluorescent Proteins Coupled to Gold Nanorods

Single-molecule imaging pushes fluorescence microscopy beyond the diffraction limit of traditional microscopy. Such super-resolution imaging, which relies on the detection of bright, stable fluorescent probes to achieve nanometer-scale resolution, is often hindered in biological systems by dim, blinking fluorescent proteins (FPs). Here, we use gold nanorods and single-molecule fluorescence detection to achieve plasmon-enhanced emission from intrinsically fluorescent proteins. We measure a doubled photon emission rate from the red FP mCherry and detect three times more photons before photobleaching from the photoactivatable FP PAmCherry. We further explore the effect of near-field nanorod interactions on the yellow FP mCitrine, for which the observed emission enhancements cannot overcome measurable quenching. Overall, our work indicates that plasmonic particles improve both the brightness and photostability of FPs and extends the applications of plasmon-enhanced fluorescence to the arena of biological imaging. Furthermore, because gold nanorods are nontoxic, they are promising extracellular imaging substrates for enhancing emission from FP-labeled membrane-bound proteins in live cells.