Using Patterned Arrays of Metal Nanoparticles to Probe Plasmon Enhanced Luminescence of CdSe Quantum Dots

Here we present a simple platform for probing plasmon enhanced photoluminescence (PL) of quantum dots by confocal microscopy. In this study, self-assembled monolayers of silane-derivative molecules were patterned onto the oxidized GaAs surfaces to direct the attachment of Au or Ag nanoparticles onto the surface. Following the directed binding of metal nanoparticles (MNPs), a layer-by-layer deposition of oppositely charged polymers was used to create films with varying thickness by controlling the numbers of deposited layers. CdSe quantum dots (QDs) of ∼4 and 5.5 nm in diameter with 16-mercaptohexadecanoic acid as a surfactant were then adsorbed onto the outermost polymer layer via electrostatic interactions. Using confocal fluorescence microscopy, the enhanced PL from the CdSe over the Au or Ag nanoparticle patterns could be imaged directly and scaled against the regions with no Au or Ag nanoparticles, and the luminescence of the GaAs (as an internal standard) for different CdSe-metal separations. By using a pattern, PL enhancement as a function of particle-CdSe spacing can be readily probed all on a single platform, where the QDs over MNPs and not over MNPs can be directly compared in the same dielectric environment. The observed luminescence as a function of metal-QD separation can be readily fit to a combined model of metal-fluorophore fluorescence quenching and local electric field enhancement.