Characterization of an electrochemical mercury sensor using alternating current, cyclic, square wave and differential pulse voltammetry

• An electrochemical Hg(II) sensor based on T–Hg(II)–T sensing motif was fabricated.
• A methylene blue-modified DNA probe was used to fabricate the sensor.
• Sensor performance was evaluated using ACV, CV, SWV, and DPV.
• The sensor behaves as a “signal-off” sensor in ACV and CV.
• The sensor behaves as either a “signal-on” or “signal-off” sensor in SWV and DPV.

Here we report the characterization of an electrochemical mercury (Hg2+) sensor constructed with a methylene blue (MB)-modified and thymine-containing linear DNA probe. Similar to the linear probe electrochemical DNA sensor, the resultant sensor behaved as a “signal-off” sensor in alternating current voltammetry and cyclic voltammetry. However, depending on the applied frequency or pulse width, the sensor can behave as either a “signal-off” or “signal-on” sensor in square wave voltammetry (SWV) and differential pulse voltammetry (DPV). In SWV, the sensor showed “signal-on” behavior at low frequencies and “signal-off” behavior at high frequencies. In DPV, the sensor showed “signal-off” behavior at short pulse widths and “signal-on” behavior at long pulse widths. Independent of the sensor interrogation technique, the limit of detection was found to be 10 nM, with a linear dynamic range between 10 nM and 500 nM. In addition, the sensor responded to Hg2+ rather rapidly; majority of the signal change occurred in <20 min. Overall, the sensor retains all the characteristics of this class of sensors; it is reagentless, reusable, sensitive, specific and selective. This study also highlights the feasibility of using a MB-modified probe for real-time sensing of Hg2+, which has not been previously reported. More importantly, the observed “switching” behavior in SWV and DPV is potentially generalizable and should be applicable to most sensors in this class of dynamics-based electrochemical biosensors.

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