Signal-enhancement by Nanostructures

Single molecule fluorescence microscopy (SMFM) has been evolved into a diversified tool-box that widely used in bioscience. It enables the faithful detection and analysis of single fluorescent molecules which offers abundant information towards functional mechanisms in biosystems. Number of photons collected through the detector dominates the precision of SMFM. Metal induced fluorescence enhancement (MIFE) takes advantage of the enhanced local fields around plasmonic nanostructure to increase the excitation and modulate the emission of fluorophores in proximity. Literally 2-3 orders of magnitude enhancement have been achieved through various shapes of nanostructures (nanoparticles, nanodimers and aggregates etc.). 

Here, we offered a creative method to enhance single molecule fluorescence quantum efficiency. Through multi-modes coupling in the asymmetric nanoantenna, coordination between radiation and non-radiation in spectra is broken thus dissipation is minimized without reducing quantum efficiency. Also, energy coupled to the antenna is increased results from the increased near field in the asymmetric antenna. Our work demonstrates a general strategy to modulate emission rate based on multi-modes coupling in nanoantenna.