Voltammetric determination of the antimalarial drug chloroquine using a glassy carbon electrode modified with reduced graphene oxide on WS2 quantum dots.

A voltammetric method is described for the determination of chloroquine (CQ) and validated simultaneously by two techniques and in three different conditions. The WS2 quantum dots (WS2 QDs) were synthesized by a hydrothermal method and then placed on reduced graphene oxide (rGO) sheets. The resulting composite material was then deposited on a glassy carbon electrode (GCE) where it showed excellent electroactivity. The modified GCE responds to chloroquine at a typical potential maximum of 1.2 V (vs. AgCl/Ag). Techniques including cyclic voltammetry and differential pulse voltammetry were tested. Features of merit include (a) a wide linear response (in the 0.5 μM to 82 μM CQ concentration range), (b) an electrochemical sensitivity of 0.143-0.90 μA·μM-1·cm-2), and a 40-120 nM limit of detection (at S/N = 3). The sensor has excellent selectivity even in the presence of potentially interfering biological compounds. Responses were tested in phosphate buffer, human serum and pharmaceutical formulations, and no cross reactivity or matrix effects were found. In all the three cases, quite satisfactory recoveries were obtained. Graphical abstract Schematic representation of the mechanism for electro-oxidation of chloroquine on a glassy carbon electrode modified with an rGO@WS2 quantum dot composite. The sensor displays enhanced electrocatalytic activity towards chloroquine. The method was validated in biological samples and pharmaceutical formulations.