A turn-on fluorescent probe for Hg2+ detection by using gold nanoparticle-based hybrid microgels

Hybrid microgels with Au nanoparticles (AuNPs) immobilized in poly( N -isopropylacrylamide- co -2-(dimethylamino)ethylmethacrylate) (P(NIPAM- co -DMA)) microgels have been prepared. The as-synthesized hybrid microgels showed excellent thermo- and pH-responsive properties and high stabilities. 1-pyrenebutyric acid (PBA) molecules were then adsorbed on the AuNP surfaces via electrostatic interactions to form PBA-AuNPs/P(NIPAM- co -DMA) composites that were used as probes for the detection of Hg 2+ . The fluorescence of PBA was effectively quenched through fluorescence resonance energy transfer between AuNPs and PBA molecules. However, the addition of Hg 2+ ions caused the fluorescence turn-on dramatically and 16 times fluorescence enhancement was obtained, which is attributed the fact that Hg 2+ ions replace the adsorbed PBA molecules. Under the optimal conditions, the fluorescence intensity was proportional to the concentration of Hg 2+ ions in the range of 0.16–1.60   μM with a detection limit of 31   nM. Meanwhile, some other metal ions did not interfere with the detection of Hg 2+ , suggesting a good selectivity for Hg 2+ ions sensing.