A novel electrochemical biosensor for Hg2+ determination based on Hg2+-induced DNA hybridization

In this paper, a novel electrochemical biosensor for Hg2+ determination based on Hg2+-induced DNA hybridization is reported. A pair of oligonucleotides with seven strategically placed thymine–thymine (T–T) mismatched bases was introduced. Firstly, one oligonucleotide (P1) modified with hexanthiol at 5-terminal was immobilized on a screen-printed gold electrode (SPGE) via self-assembly. Then the other oligonucleotide (P2) tagged with a ferrocene derivative as electroactive indicator was able to hybridize with P1 by forming thymine–Hg2+–thymine (T–Hg2+–T) complexes in the presence of Hg2+, providing a detectable electrochemical signal of the ferrocene derivative. However, when Hg2+ was absent, the two oligonucleotides could not hybridize due to the T–T mismatched bases, and P2 could not be fixed on the electrode surface, with the indicator signal disappearing. Experimental results indicate that the proposed biosensor offers linear responses on Hg2+ concentration in the range of 10–0.001 μM, with a detection limit of 0.6 nM (S/N = 3). This new Hg2+-induced DNA hybridization strategy is demonstrated valid and efficient to detect trace Hg2+ with high sensitivity and good selectivity.