Ultrafast, Selective, and ppb Level In Vitro Electrochemical Sensing of Dopamine in a Simulated Interfering Environment: Comparative Study on the Effect of Carrier Type of Electrode Materials

In order to carry out a comparative study on the effect of conduction type of electrode materials on the enzyme-less electrochemical sensing of dopamine and serotonin, three different electrode combinations were prepared on fluorine-doped tin oxide (FTO)-coated glass substrates. The electrodes were FTO/In2O3 (ITO) (n-type), FTO/Ni2O3 (p-type), and FTO/ITO/Ni2O3 (n-p junction), which were deposited using direct current (DC) sputtering and electrochemical techniques. The developed electrode materials were thoroughly characterized, both structurally and electrochemically. An actual test environment was simulated by taking a series of electroactive interfering agents to explore the in vitro electrochemical sensing performance of the developed electrode prototypes toward dopamine and serotonin. The results indicated that the developed electrodes were quite selective toward dopamine, where ITO/Ni2O3 showed the best performance. Ultrafast response (9.0 ms) even toward a very low (100 nM, 18.96 ppb) concentration of dopamine with a notably high value of sensitivity (5.03 μA μM–1 cm–2) and a very low limit of detection in the nanomolar/ppb order were exhibited by the FTO/Ni2O3 electrode. The reliability study was carried out with respect to electrochemical performance, phase purity, and structural properties after rigorous dopamine sensing by the electrodes, and the results were quite encouraging. Only 1.7% degradation in the peak current density was observed for the ITO/Ni2O3 electrode even after the 50th cycle of sensing measurements. Real sample analysis with healthy adult human male urine was also carried out using the best performer ITO/Ni2O3 electrode, which yielded a significantly high rate of recovery. The experimental data pave the path for this FTO/Ni2O3 electrode prototype for real-life applications.