Ultrasensitive electrochemical sensor for Hg2+ by using hybridization chain reaction coupled with Ag@Au core–shell nanoparticles

A novel electrochemical biosensor for Hg 2+ detection was reported by using DNA-based hybridization chain reaction (HCR) coupled with positively charged [email protected] core-shell nanoparticles ((+) [email protected] CSNPs) amplification. To construct the sensor, capture probe (CP ) was firstly immobilized onto the surface of glass carbon electrode (GCE). In the presence of Hg 2+ , the sandwiched complex can be formed between the immobilized CP on the electrode surface and the detection probe (DP) modified on the gold nanoparticles (AuNPs) based on T-Hg 2+ -T coordination chemistry. The carried DP then opened two ferrocene (Fc) modified hairpin DNA (H 1 and H 2 ) in sequence and propagated the happen of HCR to form a nicked double-helix. Numerous Fc molecules were formed on the neighboring probe and produced an obvious electrochemical signal. Moreover, (+) [email protected] CSNPs were assembly onto such dsDNA polymers as electrochemical signal enhancer. Under optimal conditions, such sensor presents good electrochemical responses for Hg 2+ detection with a detection limit of 3.6   pM. Importantly, the methodology has high selectivity for Hg 2+ detection.