Copper enhanced guanine electrochemical signal for nucleic acids detection in municipal tertiary wastewater

An electroanalytical method is developed for guanine detection based on its electrochemical oxidation on a clay-modified carbon paste electrode (clay-CPE). The electrochemical guanine signal is found to be significantly enhanced upon its complexation with Cu2+ ions. Cu2+-guanine complex formation is studied using UV–Vis spectroscopy and electrochemical pulse voltammetry at different ratios, with 1:2 Cu2+:guanine found to be the optimal stoichiometry. The clay modifier and the electrode are fully characterized using electron microscopy, Fourier-transform infrared, X-ray photoelectron and X-ray fluorescence spectroscopies, and X-ray diffractometry. The analytical method is fully optimized regarding the electrolyte, technique, and electrochemical parameters. A calibration curve is built obtaining a linear range of 0.1–45 µM, a limit of detection of 0.16 µM, a limit of quantification of 0.54 µM, and a sensitivity of 1.1 µA/µM, which are among the best reported so far and achieved with an environmentally friendly and low-cost method. Our system is very selective with minimal interference in the presence of interferents with concentrations as high as 100× that of guanine. The Cu2+-mediated clay-CPE-based analytical method is applied for the detection of nucleic acid in real-life wastewater, which is critical to achieving efficient wastewater treatment. This demonstrates the applicability of our method for environmental purposes and opens the door for other applications as well, such as diagnostics.