In situ electrochemical synthesis of reduced graphene oxide-cobalt oxide nanocomposite modified electrode for selective sensing of depression biomarker in the presence of ascorbic acid and dopamine

We report the preparation of reduced graphene oxide (RGO)/cobalt oxide (Co₃O₄) nanocomposite by a simple in situ electrochemical approach and its application towards the trace level selective determination of serotonin in the presence of ascorbic acid and dopamine. Simultaneous electrochemical reduction of graphene oxide (GO) to RGO and electrodeposition of Co₃O₄ has been achieved onto the glassy carbon electrode (GCE) surface. Raman and XRD studies confirmed the presence of RGO/Co₃O₄ nanocomposite formation. Scanning electron microscope (SEM) image shows that the presence of Co₃O₄ nanoflakes over the entire surface of wrinkled thin graphene nanosheets. The electro-oxidation of serotonin has been assessed by cyclic voltammetry and differential pulse voltammetry (DPV) in physiological pH conditions. Interestingly, the oxidation peak current (I_p) of serotonin at GCE/RGO/Co₃O₄ is 4.1 fold higher than that observed at GCE/RGO and 2.4 fold higher than that observed at GCE/Co₃O₄ modified electrode. A DPV serotonin sensor with a very low detection limit of 48.7 nM and a high sensitivity of 2.2 mA mM^− 1 cm^− 2 has been demonstrated using the as prepared GCE/RGO/Co₃O₄ modified electrode. A comparison of the sensor performance with previous literature clearly shows the superior performance of the fabricated sensor. In addition, the fabricated sensors detect serotonin in vitro directly from diluted blood serum samples.