Electrochemical Detection of Guanine-methylation Using Glassy Carbon Electrode

Abstract

This work presents a study of the electrochemical oxidation of 7-methylguanine (7-mGua) in aqueous solution at glassy carbon electrode by cyclic voltammetry, differential pulse voltammetry, square wave voltammetry and electrochemical impedance spectrometry. The anodic behaviour of 7-mGua was compared with the electro-oxidation of guanine and 7-methylguanosine. The results demonstrated that the methyl and ribose groups are not electroactive but strongly influence the oxidation mechanism of these species. The oxidation of 7-mGua occurred in a single pH-dependent step, with the withdrawal of two electrons and two protons of C8, to form 8-oxo-7-methylguanine, while the electro-oxidation of 7-methylguanosine also occurred in a single pH-dependent step, however, with the withdrawal of one electron and one proton of C8 to form a hydroxylated product, since its oxidation to 8-oxo-7-methylguanosine is hindered by the presence of the pendant groups. In addition, the oxidation of 7-mGua was investigated in the presence of DNA and DNA-bases, leading to the conclusion that the formation of 7-mGua, from an interaction of DNA with an alkylating agent, would cause an increase on the deoxyguanosine peak current of the DNA-biosensor, with no interference of any free DNA bases, which demonstrated that DNA-electrochemical biosensors find application on detecting DNA methylation, opening a new avenue for applications of DNA biosensors.