Plasmon-Enhanced Quantum Dot Fluorescence Induced by Brownian Motion

Metal-enhanced fluorescence has been extensively studied over the past three decades due to numerous opportunities for enhanced fluorescence sensing and imaging in microfluidics and medical diagnostics. Since the interaction between plasmonic nanoparticles and quantum dots (QDs) is the near-field phenomenon, most of past studies employed dielectric spacers to maintain the nanoscale interparticle distance. In the present study, however, we investigate the enhanced fluorescence from QDs that are mixed with plasmonic nanostructures, such as gold nanoshell (GNS), in the aquatic medium without confining inter-particle distances. Although the near-field interaction could not occur according to the distance estimation based on the particle concentrations, the experimental results indicate that the QD fluorescence can be greatly enhanced. A simple two-dimensional model based on Monte Carlo simulation reveals that there exist considerable probability that QDs reach the near-field region of GNSs due to the thermally induced Brownian motion. The results obtained from this study will facilitate the development of QD-mediated thermometry and ultimately enable image-guided deep-tissue thermal therapy.