Graphene quantum dot/Ag-based metal–organic framework nanocomposite-modified carbon paste electrode for simultaneous determination of diazepam, dopamine, clonazepam and adrenaline in real samples

This research introduces a novel nanocomposite comprising graphene quantum dots (GQDs) and a silver-based metal–organic framework (Ag-MOF), referred to as GQD–Ag-MOF, which was utilized as a modifier in order to develop an electrochemical sensor for the quantification of diazepam. The as-prepared nanocomposite was characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), dynamic light scattering (DLS), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The results of cyclic voltammetry (CV) experiments demonstrated that the GQD–Ag-MOF-modified carbon paste electrode (GQD–Ag-MOF/CPE) demonstrated excellent electrocatalytic activity for the oxidation of diazepam. Additionally, the electron transfer coefficient (α) for diazepam oxidation at the sensor surface was investigated using the CV technique. The diffusion coefficient of diazepam was determined via chronoamperometry, and the analytical performance of the proposed sensor was evaluated using electrochemical impedance spectroscopy (EIS). By means of square wave voltammetry (SWV), a linear response range of 0.1–1300.0 μM and a limit of detection of 0.03 μM for diazepam were obtained. The developed sensor was utilized to determine diazepam, dopamine, clonazepam, and adrenaline simultaneously, and the recorded SW voltammograms showed four well-separated anodic oxidation peaks at 202.7, 319.2, 466.2, and 689.2 mV, respectively. Furthermore, linear ranges of 175.3–526.0 μM for diazepam, 16.0–48.0 μM for dopamine, 12.3–37.0 μM for clonazepam, and 4.1–15.1 μM for adrenaline were obtained. In conclusion, the developed sensor was successfully utilized for the quantification of these drugs in medicinal and biological samples.