Label-free electrochemical DNA biosensor for guanine and adenine by ds-DNA/poly(L-cysteine)/Fe3O4 nanoparticles-graphene oxide nanocomposite modified electrode.

In this study, we aim to design a simple and effective electrochemical DNA biosensor based on a carbon paste electrode modified with ds-DNA/poly(L-cysteine)/Fe3O4 nanoparticles-graphene oxide (ds-DNA/p(L-Cys)/Fe3O4 NPs-GO/CPE) for sensitive detection of adenine (A) and guanine (G). The electrocatalytic oxidation of A and G on the electrode was explored by differential pulse voltammetry (DPV) and cyclic voltammetry (CV). This sensor shows separated and well-defined peaks for A and G, by which one can determine these biological bases individually or simultaneously. The ds-DNA/p(L-Cys)/Fe3O4 NPs-GO/CPE exhibited an increase in peak currents and the electron transfer kinetics and decrease in the overpotential for the oxidation reaction of A and G. Under the optimal conditions a linear relationship is figured out between the peak current and the analytes' concentrations on a range of 0.01-30.0μM and 0.01-25.0μM for simultaneous determination of A and G, with detection limits of 3.48 and 1.59nM, respectively. As well as, individually determination is resulted two linear concentration ranges of 0.01-30.0μM for A and 0.01-25.0μM for G with detection limits of 3.90 and 1.58nM for A and G, respectively. The proposed biosensor exhibited some advantages in terms of simplicity, rapidity, high sensitivity, good reproducibility and long-term stability. Furthermore, the measurements of thermally denatured single-stranded DNA were carried out and the value of (G + C)/(A + T) of DNA was calculated as about 0.77 for various DNA samples. This study also ascertained that the proposed biosensor can be profitable to evaluate DNA bases damage.