Turn on'' and label-free core-shell Ag@SiO2 nanoparticles-based metal-enhanced fluorescent (MEF) aptasensor for Hg2+

A turn on and label-free fluorescent apasensor for Hg2+ with high sensitivity and selectivity has been demonstrated in this report. Firstly, core-shell Ag@SiO2 nanoparticles (NPs) were synthetized as a Metal-Enhanced Fluorescent (MEF) substrate, T-rich DNA aptamers were immobilized on the surface of Ag@SiO2 NPs and thiazole orange (TO) was selected as fluorescent reporter. After Hg2+ was added to the aptamer-Ag@SiO2 NPs and TO mixture buffer solution, the aptamer strand can bind Hg2+ to form T-Hg2+-T complex with a hairpin structure which TO can insert into. When clamped by the nucleic acid bases, the fluorescence quanta yield of TO will be increased under laser excitation and emitted a fluorescence emission. Furthermore, the fluorescence emission can be amplified largely by the MEF effect of the Ag@SiO2 NPs. The whole experiment can be finished within 30 min and the limit of detection is 0.33 nM even with interference by high concentrations of other metal ions. Finally, the sensor was applied for detecting Hg2+ in different real water samples with satisfying recoveries over 94%.