Electrochemical Determination of 6-thioguanine and Its Interaction with DNA Oligonucleotides Using Disposable Graphite Pencil Electrodes

Disposable graphite pencil electrodes were used in this study for the electrochemical determination of 6-thioguanine using its interaction with a single stranded Oligo (A)₂₅ composed of twenty-five adenine (A) bases or double stranded Oligo (A)₂₅–Oligo (T)₂₅, a hybrid form of Oligo (A)₂₅ and Oligo (T)₂₅ composed of twenty-five thymine (T) bases. The surface interaction was evaluated by monitoring the changes of the oxidation signals of 6-thioguanine and adenine. The electrochemical measurements were performed using differential pulse voltammetry, cyclic voltammetry, and electrochemical impedance spectroscopy. The experimental conditions, including the concentration of 6-thioguanine and its period of interaction with single stranded Oligo (A)₂₅ or double stranded Oligo (A)₂₅–Oligo (T)₂₅, were optimized by observing the changes in the 6-thioguanine and adenine oxidation currents by differential pulse voltammetry. The detection limit was determined to be 0.24 µM across the useful linear concentration range from 1 to 4 µM 6-thioguanine. The reported single-use graphite sensor provides a cost effective, rapid, and sensitive detection approach for the electrochemical characterization of the interaction between DNA and 6-thioguanine.