Cost-Effective Electrochemical Activation of Graphitic Carbon Nitride on the Glassy Carbon Electrode Surface for Selective Determination of Serotonin.

A simple one-step electrochemical deposition/activation of graphitic carbon nitride (g-C3N4) is highly desired for sensor configurations and remains a great challenge. Herein, we attempt an electrochemical route to exfoliate the g-C3N4 nanosheets in an aqueous solution of pH 7.0 for constructing a sensor, which is highly sensitive for the detection of serotonin (5-HT). The significance of our design is to exfoliate the g-C3N4 nanosheets, a strong electrocatalyst for 5-HT detection. Investigations regarding the effect of neutral pH (pH 7.0) on the bulk g-C3N4 and g-C3N4 nanosheets, physical characterization, and electrochemical studies were extensively carried out. We demonstrate that the g-C3N4 nanosheets have a significant electrocatalytic effect for the 5-HT detection in a dynamic linear range from 500 pM to 1000 nM (R2 = 0.999). The limit of detection and sensitivity of the designed 5-HT sensor was calculated to be 150 pM and 1.03 µA µM-1 cm-2, respectively. The proposed sensor has great advantages such as high sensitivity, good selectivity, reproducibility, and stability. The constructed g-C3N4 nanosheets-based sensor platform opens new feasibilities for the determination of 5-HT even at the picomolar/nanomolar concentration range.

Electrochemical reactive oxygen species detection by cytochrome c immobilized with vertically aligned and electrochemically reduced graphene oxide on a glassy carbon electrode.

A new amperometric biosensor for hydrogen peroxide (H2O2) and superoxide anion (SO) has been developed. The biosensor developed uses cytochrome c (Cyt c) modified glassy carbon electrodes coupled with electrochemically reduced graphene oxide (ErGO). To immobilize Cyt c, the "one step" electrochemical deposition of vertically aligned and ErGO (VAErGO) has been performed by using a pulse reverse technique, thus resulting in a very simple and efficient system. The well-established vertical alignment of ErGO was confirmed by atomic force microscopy and the electrochemical characteristics of the biosensor were investigated by cyclic voltammetric, electrochemical impedance spectroscopy and amperometric techniques. The surface coverage (Γ) of immobilized Cyt c was effectively increased by the vertical alignment of ErGO and found to be 1.03 × 10-10 mol cm-2. The direct electron transfer property of Cyt c was also improved by VAErGO and the heterogeneous electron transfer rate constant (ket) was estimated to be 6.40 s-1. To detect H2O2 and SO, amperometric measurements were carried out at different operating potentials (0.0 V vs. Ag/AgCl for H2O2 and +0.2 V for SO). The sensitivity and detection limit for H2O2 were found to be 46.3 µA mM-1 cm-2 and 2.3 µM, and for SO were found to be 32.1 µM nA-1 cm-2 and 6.84 nM s-1, respectively. Additionally, the designed biosensor exhibited strong anti-interference ability and satisfactory reproducibility.