Comparison between electrochemical and photoelectrochemical detection of dopamine based on titania-ceria-graphene quantum dots nanocomposite

In this study, titania-ceria-graphene quantum dot (TC-GQD) nanocomposite was synthesized by hydrothermal method for the first time. The prepared nanomaterials were characterized by XRD, FTIR dynamic light scattering (DLS), FESEM, HRTEM, and EDX spectroscopy along with elemental mapping. The synergistic effect of the nanocomposite components was studied by diffuse reflectance spectroscopy (DRS) and electrical conductivity meter. The results showed that band gap of TC-GQD nanocomposite was shifted to visible lights relative to its components (1.3 eV), and electrical conductivity of the sample was significant increased to 89.5 μS cm-1. After chemical and physical characterization, prepared new nanocomposites were used to design a new electrochemical (EC) and photoelectrochemical (PEC) dopamine (DA) sensors. In both EC and PEC methods effecting experimental parameters were optimized. Due to the synergic effect of the nanocomposite components, an outstanding photocurrent response was observed for DA based on PEC sensor. A linear calibration curve with a lower detection limit of 22 nM DA, and sensitivity of 13.8 mA/mM(DA), in a wider range of 0.3-750 μM DA, was obtained for TC-GQD/GCE electrode in PEC. While, the TC-GQD/GCE electrode detected DA in the range of 1-500 μM DA, with two linear calibration curve, detection limit of 0.22 μM DA, and sensitivity of 4.9 mA/mM(DA), in the EC. Observed results from EC and PEC sensors are presented and compared.