Graphene oxide /Graphene Quantum Dots: A platform for probing ds-DNA-Dimethoate Interaction and Dimethoate Sensing

A nanocomposite of graphene oxide and graphene quantum dots (GO@GQDs) were used for the first time to probe the ds-DNA-dimethoate (DMT) interaction and detect the DMT at a trace level. Graphene quantum dots were electrodeposited onto a glassy carbon electrode (GCE), followed by casting a graphene oxide layer. This platform was employed to adsorb the ds-DNA to fabricate DNA biosensors (ds-DNA/GO@GQDs/GCE). Microscopic and electrochemical characterizations of the modified electrodes were performed. The GO/GDQs/GCE platform exhibited remarkable electrocatalytic oxidation of DMT from acetate and phosphate buffers. The oxidation process of DMT was pH-dependent and irreversible, proceeding under the mixed adsorption and diffusion-controlled mechanism. The interaction of salmon sperm double-strand DNA (ss-dsDNA) with DMT was investigated using differential pulse voltammetry and UV/vis spectroscopy. Mixed binding modes of intercalation and the electrostatic were ascertained for the interaction of DMT to dsDNA. Such a result was confirmed from the voltammetric data of single-stranded DNA (ssDNA) and the ionic strength study. The UV–Vis study has also supported that finding.

The indirect DMT detection is verified by the drop in DNA oxidation signals or increasing DPV peak currents conducted from [Fe(CN)6]3−/4− probe. The decrease in the DNA peak currents linearly correlated to DMT linear range of 10−15 M to 10−10 M with a limit of detection about 10−15 M. The same detection limit was achieved through the increasing the peak current of [Fe(CN)6]3−/4− at DMT linear range of 10−15 to 10−12 M.

The mechanism of DMT oxidation on GO/GQDs/GCE was proposed and confirmed by forming a self-assembled layer (SAM) of DMT onto the gold electrode (AuE). The surface DMT undergoes anodic oxidation with Ep close to the one recorded at GO/GQDs modified surface, referring that the amide group is only possible to oxidize, and the sulfur-containing groups are involved in SAM. The DMT-SAM/AuE would present additional evidence for the surface analysis of DMT-DNA interaction where a change in the DMT peak current upon adding DNA was recorded. ds-DNA-GO@GQDs/GCE sensor exhibits a rapid response, reproducibility, a low detection limit, and high selectivity. The present work may expand the use of GO/GQDs modifiers in the field of electrochemical sensors.