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

A novel electrochemical biosensor for Hg2+ detection was reported by using DNA-based hybridization chain reaction (HCR) coupled with positively charged Ag@Au core-shell nanoparticles ((+)Ag@Au CSNPs) amplification. To construct the sensor, capture probe (CP ) was firstly immobilized onto the surface of glass carbon electrode (GCE). In the presence of Hg2+, 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-Hg2+-T coordination chemistry. The carried DP then opened two ferrocene (Fc) modified hairpin DNA (H1 and H2) 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, (+)Ag@Au CSNPs were assembly onto such dsDNA polymers as electrochemical signal enhancer. Under optimal conditions, such sensor presents good electrochemical responses for Hg2+ detection with a detection limit of 3.6 pM. Importantly, the methodology has high selectivity for Hg2+ detection.