Highly sensitive and selective electrochemical detection of Hg2+ through surface-initiated enzymatic polymerization

A Hg 2+ electrochemical biosensor is developed by integrating thymine–Hg 2+ –thymine (T–Hg 2+ –T) base pairs for the high selectivity with surface-initiated enzymatic polymerization (SIEP) for signal amplification . The fabrication begins with the covalent conjugation of capture DNA probe labeled with thiol at its 3′terminal onto the gold electrode. The presence of Hg 2+ leads to DNA hybridization, in which complementary DNA was captured onto the biosensor surface, which subsequently catalyzed the addition of deoxynucleotides (dNTP) containing biotinlated 2′-deoxyadenosine 5′-triphosphate (biotin-dATP) by terminal deoxynucleotidyl transferase (TdT). The binding between biotin and strepavidin leads to the attachment of a large number of strepavidin functionalized silver nanoparticles (strepavidin-AgNPs), which could generate electrochemical stripping signal of silver to monitor the concentration of Hg 2+ in KCl solution. Through utilizing the T–Hg 2+ –T selectivity and SIEP amplification, this assay method can detect aqueous Hg 2+ with a wide linear range from 0.05   nM to 100   nM and a detection limit of 0.024   nM. The application of this sensor in the analysis of drinking water demonstrates that the proposed method works well for real samples.