Metal-enhanced fluorescence-based multilayer core–shell Ag-nanocube@SiO2@PMOs nanocomposite sensor for Cu2+ detection

A silver nanocube (Ag NC) nanoparticle-enhanced fluorescent nanocomposite was developed. The designed nanocomposite contained an Ag NC core of 50 nm in size as enhancer, the 10 nm silica interlayer, and outer shell-periodic mesoporous organosilicas (PMOs) which incorporated the bis(rhodamine Schiff-base derivative) siloxane groups. Little fluorescence emission of nanocomposites was observed due to the existence of spirolactam in the rhodamine derivative, however, upon the addition of Cu2+, the fluorescence emission intensity increased dramatically, which resulted from ring-opening of the spirolactam in the rhodamine moieties. We showed the effect of using an Ag NC core on the fluorescence emission intensity of the novel system. The emission intensity was approximately 3-fold higher for Ag-nanocube@SiO2@PMOs than the control sample prepared by etching the silver core away with iodide. Moreover, the metal-enhanced fluorescence (MEF) mechanism in this system was investigated through measuring the fluorescence lifetime. In addition, the designed core–shell Ag-nanocube@SiO2@PMOs nanocomposite could act as a sensitive and selective sensor to detect the Cu2+, and we have been expecting that the detection limit would be reduced by reaping benefits from the plasmon resonance of Ag NC core in this nanocomposite system.