Green Carbon Quantum Dots Based Electrochemical Sensors for Analysis of Neurotransmitters

Abstract

The study described the synthesis and characterization of carbon-based quantum dots/copper oxide nanocomposite prior to the modification of a glassy carbon electrode for neurotransmitters detection (dopamine (DA), epinephrine (EP), and norepinephrine (NE)). The two carbon-based quantum dots were prepared from pencil graphite and banana peel precursors and tagged CQDs and bCQDs, respectively. The spectroscopic and microscopic characterization of the carbon based quantum dots (CQs) were achieved through Fourier Transform infrared spectroscopy (FT-IR), UV-visible spectroscopy, x-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The preparation of the banana peel precursor used for the green carbon quantum dots (bCQDs) synthesis, green carbon quantum dots (bCQDs), and carbon quantum dots from pencil graphite precursor (CQDs) was monitored with thermogravimetric analysis (TGA). The electrochemical characterization of the quantum dots (CQDs, bCQDs), copper oxide nanoparticles (CNPs), and the nanocomposites (CQDs/CNPs and bCQDs/CNPs) was done with electrochemical impedance spectroscopy (EIS). Bare GCE and GCE modified with these materials (GCE/CQDs, GCE/bCQDs, GCE/CNPs, GCE/bCQDs/CNPs, and GCE/CQDs/CNPs) in the presence of 5 mM ferricyanide/ferrocyanide ([Fe(CN)6]3-/4-) redox probe were used for electrochemical characterization. The EIS data showed that the composites have lower charge transfer resistance than the individual nanomaterials. The superior electronic properties of the composite relative to the individual nanomaterials show that the combination of the nanomaterials for the composite formation offered a synergy that results in better electron transport properties. The electroanalysis of the analytes (DA, EP, and NE) at the bare and modified electrodes done with cyclic voltammetry (CV) showed that the analytes experienced better electrocatalytic oxidation at the composites modified electrodes (GCE/bCQDs/CNPs and GCE/CQDs/CNPs). The EIS analysis of the analytes at the bare and modified electrode supported the superior electron transfer between the analytes and the two sensors compared to other electrodes. ...