In-situ Investigation of Surface Plasmon Resonance Enhanced Fluorescence Propertyduring Deposition of Gold Quantum Dots on Polyelectrolyte Multilayers

摘要

In this study, we present in-situ investigation of surface plasmon enhanced fluorescence emission from thegold quantum dots (AuQDs) during the deposition on polyelectrolyte multilayers ultrathin films. When thediameter of gold particles becomes less than 2 nm, they are called gold quantum dots (AuQDs) or goldnanoclusters, on which localized surface plasmons cannot be excited. Instead, the AuQDs exhibit quantumconfinement effects, meaning that the number of gold atoms in the AuQDs determines the wavelength of thefluorescence emission in the visible range. This implies that AuQDs can harvest light from the UV regionand convert it into visible light.By using the quenching / enhancement phenomenon, AuQDs have beenapplied to biosensor, organic electronic devices, and so forth. In this work, we studied the quenching /enhancement phenomenon of AuQDs by controlling the thickness of polyelectrolyte multilayers ultrathinfilms (intermediate layer) between the metal and AuQDs. Poly (diallyldimethylammonium chloride)(PDADMAC) and poly (sodium 4-styrenesulfonate) (PSS) were used as the polyelectrolyte layers. First, thepolyelectrolyte multilayer was deposited on an aluminum surface using a layer-by-layer (LbL) adsorptiontechnique by sequentially dipping the aluminum-coated high refractive index glass substrate into an aqueoussolution of the positively charged PDADMAC and negatively charged PSS. Finally, a monolayer of AuQDsis deposited on PDADMAC/PSS films by spin-coating technique. The fluorescence quenching / enhancementof AuQDs by controlling the thickness of PDADMAC/PSS bilayers was monitored by surface plasmonresonance enhanced fluorescence measurement as schematically shown in Fig. 1. As the number ofPDADMAC/PSS films increased up to 12 layers, the fluorescence intensity of the AuQDs increased. Then,the fluorescence intensity decreased when the number of layer became more than 12 layers. As shown in Fig.2, the optimum distance between the AuQDs and aluminum layer is 12 layers, i.e. ca. 20 nm. Further studiesrelating to H_2O_2 sensing technique based on the fluorescence quenching and wavelength shift of AuQDs withAgNPs are under way.