A novel graphene-DNA biosensor for selective detection of mercury ions

A novel electrochemical biosensor for sensitive and selective detection of mercury (II) ions (Hg²⁺) based on a DNA grafted graphene is proposed. Graphene oxide (GO) was reduced by dopamine, and then the single-strand probe DNA modified at the 5'-end with an alkylamino modifier (NH₂-ssDNA) was grafted on the reduced graphene oxide (RGO) surface via Michael addition reaction. In the presence of Hg²⁺, the target DNA with four thymine-thymine (T-T) mismatches would hybridize with the probe DNA on the glassy carbon electrode (GCE) through T-Hg²⁺-T coordination chemistry. The hybridization of the two oligonucleotides leads to the increase in the peak currents of [Ru(NH₃)₆]³⁺, which could be used for electrochemical sensing of Hg²⁺. The difference in the value of the peak currents of [Ru(NH₃)₆]³⁺ before and after DNA hybridization was linear with the concentration of Hg²⁺ in the range from 8.0×10⁻⁹ to 1.0×10⁻⁷ M with a linear coefficiency of 0.996. The detection limit was 5.0×10⁻⁹ M (S/N=3). The proposed electrochemical biosensor is rapid, convenient and low-cost for effective sensing of Hg²⁺. Particularly, the proposed method was applied successfully to the determination of Hg²⁺ in real environmental samples.