A highly selective electrochemical biosensor for Hg2+ using hemin as a redox indicator

A highly selective electrochemical biosensor for the detection of Hg2+ in aqueous solution has been developed. This sensor is based on the strong and specific binding of Hg2+ by two DNA thymine bases (T–Hg2+–T). The hemin worked as a redox indicator to generate a readable electrochemical signal. Short oligonucleotide strands containing 5 thymine (T5) were used as probe. Thiolated T5 strands were self-assembled through Au–S bonding on gold electrode. In the presence of Hg2+, the specific coordination between Hg2+ and thymine bases resulted in more stable and porous arrangement of oligonucleotide strands, so hemin could be adsorbed on the surface of gold electrode and produced an electrochemical signal, which was monitored by differential pulse voltammetry (DPV). The DPV showed a linear correlation between the signal and the concentration of Hg2+ over the range 0–2 μM (R2 = 0.9983) with a detection limit of 50 nM. The length of probe DNA had no significant impact on the sensor performance. This electrochemical biosensor could be widely used for selective detection of Hg2+.

Research highlights
► A highly selective electrochemical biosensor for Hg2+ detection.
► Strong and specific binding of Hg2+ by two DNA thymine bases.
► Hemin worked as a redox indicator.
► Thiolated T5 strands were self-assembled on gold electrode.
► DPV showed a linear correlation between the signal and Hg2+ concentration.