Electrochemical Sensor for Mercury(II) Based on Conformational Switch Mediated by Interstrand Cooperative Coordination

A novel electrochemical sensor was developed for sensitive and selective detection of mercury(II), based on thymine−Hg2+−thymine (T−Hg2+−T) coordination chemistry. This strategy exploited the cooperativity of proximate poly-T oligonucleotides in coordination with Hg2+. Ferrocene (Fc)-tagged poly-T oligonucleotides were immobilized on the electrode surface via self-assembly of the terminal thiol moiety. In the presence of Hg2+, a pair of poly-T oligonucleotides could cooperatively coordinate with Hg2+, which triggered a conformational reorganization of the poly-T oligonucleotides from flexible single strands to relatively rigid duplexlike complexes, thus drawing the Fc tags away from the electrode with a substantially decreased redox current. The response characteristics of the sensor were thoroughly investigated using capillary electrophoresis and electrochemical measurements. The results revealed that the sensor showed a sensitive response to Hg2+ in a concentration range from 1.0 nM to 2.0 μM, with a detection limit of 0.5 nM. Also, this strategy afforded exquisite selectivity for Hg2+ against a reservoir of other environmentally related metal ions, compared to existing anodic stripping voltammetry (ASV) techniques. In addition, this sensor could be implemented using minimal reagents and working steps with excellent reusability through mild regeneration procedure. It was expected that this cost-effective electrochemical sensor might hold considerable potential in on-site applications of Hg2+ detection.