Surface Plasmon Resonance Field-Enhanced Fluorescence Properties of Gold Quantum Dots on Polyelectrolyte Multilayers and Their H2O2 Sensor Application

In this work, we investigate surface plasmon field-enhanced fluorescence (SPF) emission from gold quantum dots (AuQDs) on a polyelectrolyte multilayer ultrathin film deposited onto an Al thin film. Polyelectrolyte layers of poly(diallyl dimethyl ammonium chloride) (PDADMAC) and poly(sodium 4-styrenesulfonate) (PSS) are deposited onto the Al surface using a layer-by-layer (LbL) adsorption technique. AuQDs are subsequently deposited onto the PDADMAC/PSS ultrathin films to study their fluorescence enhancement/quenching phenomenon, as monitored by SPF spectroscopy. The distance between the AuQDs and the Al thin film is controlled by the number of deposited PDADMAC/PSS LbL films. With increasing number of the PDADMAC/PSS bilayers, the fluorescence intensity of the AuQDs increases until the optimum distance between the AuQDs and Al layers is achieved. Moreover, silver nanoprisms (AgNPrs) are coated onto the AuQDs for H2O2 sensing. When the AgNPrs are present, a decrease in the fluorescence intensity of the AuQDs due to energy transfer from the AuQDs to the AgNPrs is observed. Recovery of the fluorescence intensity of the AuQDs is observed upon injection of a H2O2 solution, where the recovery of the intensity is proportional to the H2O2 concentration in the range from 1 pM to 100 nM and results from the oxidation reaction or etching of the AgNPrs. The fluorescence recovery is attributed to weakening of the quenching effect by a reduction in concentration of the AgNPrs. The proposed system exhibits strong potential for the development of H2O2 sensors.