CVD Graphene Electrode for Direct Electrochemical Detection of Double-Stranded DNA

Understanding and regulating DNA interactions with solvents and redox-active centers opens up new possibilities for improving electrochemical signals and developing adequate biosensors. This work reports the development of a modified indium tin oxide (ITO) electrode by chemical vapor deposition (CVD) of graphene for the detection of double-stranded DNA. The modified electrode shows a better electrical conductivity than ITO, as confirmed by electrochemical impedance spectroscopy (EIS), where a drastic decrease in the charge-transfer resistance, R-ct, from similar to 320 to similar to 60 omega was observed. Sequences of double-stranded genomic DNA with a different number of base pairs are evaluated through differential pulse voltammetry (DPV), using ferri/ferrocyanide ([Fe(CN)(6)](3-/4-)) as a mediator in the solution. Variations in the electrochemical response of the [Fe(CN)(6)](3-/4-) probe are observed after introducing redox inactive double-stranded DNA ions. The redox-active [Fe(CN)(6)](3-/4-) probe serves as a scaffold to bring DNA into the graphene-modified ITO electrode surface, provoking an increase in the current and a change in the potential when the number of base pairs increases. These results are confirmed by EIS, which shows a variation in the R-ct. The calibration of DPV intensity and R-ct vs. DNA base pairs (bps) number were linear in the 495-607 bps range. The proposed method could replace the nucleic acid gel electrophoresis technique to determine the presence of a DNA fragment and quantify its size.