A voltammetric biosensor for mercury(II) using reduced graphene oxide@gold nanorods and thymine-Hg(II)-thymine interaction

The presented voltammetric mercury(II) sensor is based on the specific interaction between Hg(II) ion and thymine-thymine base pairs. Reduced graphene oxide is functionalized with gold nanorods and then loaded with thionine and streptavidin (RGO@AuNR-TH-SA). A T-rich thiolated DNA (S1) is firstly immobilized on a gold electrode. In the presence of Hg (II), the T-rich biotin-DNA (biotin-S2) binds to S1 via T-Hg(II)-T interaction. Then, the RGO@AuNR-TH-SA is linked to the gold electrode by specific binding between SA and biotin-S2. This produces an electrochemical signal (at -0.208V vs. Ag/AgCl) of TH that depends on the concentration of Hg (II). The peak current increases linearly in the 1 to 200nM Hg (II) concentration range, and the detection limit is 0.24nM. The sensor is highly selective for Hg (II) over other environmentally relevant metal ions, even at concentration ratios of >1000.