Direct electrochemical synthesis of graphene nanosheets on pencil graphite electrode and decorating its surface with poly (L-methionine) for electroanalysis of acyclovir

Acyclovir (9-2-hydroxyethoxymethyl guanine, (ACV), as an inhibitor of the replication of herpes viruses, has been used effectively in the treatment of patients with herpes simplex and herpes zoster [1,2]. But due to some adverse neurotoxic and neurotoxic effects, developing sensitive and selective methods for monitoring of its concentration in biological samples is interesting [3]. In the present study, a novel, simple and one spot procedure is reported to produce graphene (Gr) on the surface of a pencil graphite electrode (PGE). The formation of Gr was achieved on the surface of PGE as the working electrode by amperometric method in sulfuric acid solution. The Gr-coated electrode was subjected to electrochemical polymerization of L-methionine resulting a polymer thin film. This modified electrode was applied to determination of ACV. The morphology and structure of the composite film were characterized using X-ray diffraction, electrochemical impedance spectroscopy and Field emission scanning electron microscopy. The results show that Gr nanosheets were successfully synthesized and poly(L-methionine) anchored on the Gr sheets. The stepwise modification of the electrode surface was followed by cyclic voltammetric (CV) using [Fe(CN)6]3-/4- as the probe. The CVs of bare PGE showed a pair of broad redox peaks with ΔEp of 170 mV, but the CVs of the poly (L-methionine)/PGE displayed higher peak currents and smaller ΔEp value (125 mV), and in the case of Gr/PGE the value ΔEp was 110 mV, and the current intensity was extraordinary enhanced with respect to that of unmodified PGE or poly(L-methionine)/PGE. Furthermore, when the poly (L-methionine)/Gr/PGE was used, the peak currents further increased to a certain degree and the ΔEp value decreased to 90 mV, which demonstrated the effective facilitation of electron transfer for [Fe(CN)6]3-/4- due to the combined action of poly (L-methionine) and Gr enhances the conductivity and catalytic activity of the modified electrode. Under the optimized conditions, the electrooxidation of ACV on the poly(L-methionine)/Gr/PGE modified electrode surface was investigated comparatively with Gr/PGE, poly(L-methionine)/PGE and bare PGE. The calibration curve was linear for ACV concentrations from 0.05 to 50 µM with a LOD value of 15 nM observed by differential pulse voltammetry. The application of the electrode for the determination of ACV in blood serum was investigated.