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

A Hg2+ electrochemical biosensor is developed by integrating thymine-Hg2+-thymine (T-Hg2+-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 Hg2+ 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 Hg2+ in KCl solution. Through utilizing the T-Hg2+-T selectivity and SIEP amplification, this assay method can detect aqueous Hg2+ 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.