Redox Indicator-Based Electrochemical DNA Detection

Screen-printed electrochemical sensors have gained considerable research interest in recent years due to their favorable properties in terms of sensitivity, analysis time, instrumentational simplicity, and cost-efficiency, which make them ideally suited for point-of-care testing applications. Electrochemical DNA sensors are of particular interest due to the important role of nucleic acids as biomarker in disease diagnostics. As a result, a wide variety of novel electrochemical DNA sensing approaches have already been developed to allow, e.g., for the detection of viral or bacterial nucleic acids, but also for the rather challenging detection of cancer-related point mutations, which requires exceptionally high level of selectivity. Many of the developed electrochemical DNA detection approaches rely on the use of DNA-binding redox indicators, the prerequisite being a different interaction of these compounds with single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). We investigated the suitability of the commonly used DNA-binding redox indicators ruthenium(III) hexaammine, methylene blue, anthraquinone-2-sulfonic acid (AQMS), and anthraquinone-2,6-disulfonic acid (AQDS) for electrochemical detection of DNA hybridization on screen-printed sensors via differential pulse voltammetry. For none of the tested redox indicators we observed a significant signal difference between ssDNA and dsDNA that would allow for detecting DNA hybridization. In contrast, a horseradish peroxidase (HRP)-based enzyme-linked electrochemical assay proved suitable for sensitive and specific target DNA detection due to the inherent advantages of enzymatic signal amplification and negligible current response in the absence of target DNA.