Experimental Study of Enhancement and Quenching of Plasmon-Controlled Fluorescence Using Quantum Dot–Plasmonic Nanoparticle Mixtures in Aqueous Medium

This article reports the enhancement and quenching of quantum dot (QD) emission for different concentrations of plasmonic nanoparticles (PNPs) by utilizing the Brownian motion-induced dynamic near-field interactions in aqueous solution. We measured the fluorescence spectrum of two types of QD-PNP mixtures. The first mixture was QDs (525 nm for emission wavelength) and gold nanoparticles dispersed in distilled water, where the emission wavelength of the QDs matches the localized surface plasmon (LSP) excitation wavelength of the gold nanoparticles. The second mixture was QDs (655 nm for emission wavelength) and silver nanoparticles dispersed in distilled water, where LSPs excited at the wavelength of 392 nm affect the excitation of the QDs. For both experiments, the QD emission spectra were monitored while changing the concentration of the PNPs from 108 to 1011 /mL for a fixed concentration of QDs at 1 × 1013 /mL. For low PNP concentrations, the QD emission was enhanced for 30 nm gold nanoparticles and 80 nm silver nanoparticles; however, for high PNP concentrations, the QD emission was always quenched. This research reveals the dependence of the QD fluorescence on the concentration of PNPs. The obtained results will be beneficial in further understanding plasmonic interactions between QDs and nanoparticles and the manipulation of QD emission, switching from enhancement to quenching or vice versa, with the alteration of nanoparticle concentration.