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 PI 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 mu M, 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. (C) 2011 Elsevier B.V. All rights reserved.