Ultrasensitive detection of Hg(II) through metal-enhanced fluorescence and hybridization chain reaction

We report a sensitive sensing strategy based on metal-enhanced fluorescence (MEF) and hybridization chain reaction (HCR). Hg2+ aptamers were immobilized on magnetic nanoparticles (NPs) and HCR process happened without Hg2+, forming long DNA chains and allowing fluorescent indicator (SYBR Green) intercalated in the double helix. After magnetic separation from test solution, positively charged Ag@SiO2 NPs were added, they were electrostatically absorbed on negatively charged DNA chains, acting as “smart dust” to enhance fluorescence signal. This design was used for Hg2+ detection and it showed high sensitivity with a limit of detection down to 25 pM. This method also exhibited good selectivity over other metal ions and was successfully applied in real water sample analyses.