Functionalization Of Graphene And Its Application For Electrochemical Determination Of Dopamine

Dopamine, one of the most significant catecholamines, belongs to the excitatory neurotransmitter family. It has a great influence on central nervous, cardiovascular and endocrine systems. Abnormal levels of dopamine may result in a variety of diseases, such as Schizophrenia, Huntington's disease, Parkinson's disease, and dementia among many others. Due to the trace concentration of dopamine in biological environment, the selective detection of dopamine has been attracted more and more attention and is becoming more challenging nowadays. Many analysis methods with higher sensitivity have been developed recently. However, these applications were greatly restricted because of complicated sample pretreatment and high running costs. Therefore, an inexpensive, simple, fast analytical method with high sensitivity and selectivity is still needed for the determination of dopamine in the field of biomedical chemistry, neurochemistry, diagnostic and pathological research.Electrochemical determination of dopamine may be a feasible and effective approach due to the high electrochemical activity of dopamine at an electrode. The method is simple, fast, low-cost, high sensitivity without time-consuming pretreatment. Uric acid (UA) and ascorbic acid (AA) are coexisted with dopamine (DA) in the extracellular fluids of the central nervous system and can be oxidized at potentials close to that of dopamine. Thus, it is still of interest to develop novel electrode materials and analytic methods to accomplish electrochemical determination of dopamine with high sensitivity and selectivity. Graphene nanosheets, a two-dimensional nanomaterial with one or several atomic layers of carbon, have been considered to be a promising candidate for fabricating electrode materials in the fields of electrochemistry and electroanalysis because of the fundamental attributes, such as unexpected stability, high specific surface area and excellent electric conductivity. However, the chemical reduced graphene oxide tends to agglomerate or precipitate and could not be redispersed in water by ultrasonication. The surface area of graphene will be greatly reduced and electric conductivity will be affected after agglomeration. To address this problem, modification of graphene oxide with different functional molecules would have to be introduced to improve their properties or extend their functions.In this research paper, the applications of two kinds of functionalized graphene modified electrodes are studied for high sensitivity and selectivity determination of dopamine. The details are categorized as follows:1. Graphene/gold nanoparticle multilayer films composed of polysodium 4-styrenesulfonate (PSS) functionalized reduced graphene oxide (RGO) and polyamidoamine (PAMAM) dendrimer stabilized gold nanoparticles (AuNPs) were fabricated using the electrostatic layer-by-layer (LBL) self-assembly technique on a glassy carbon electrode (GCE) modified with a first layer of poly(diallyldimethylammonium chloride) (PDDA). The film assembly, the electrochemical property as well as the electrocatalytic activity toward the oxidation of dopamine were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). Electrochemical studies exhibit that the LBL assembled RGO/AuNPs films possess an excellent sensing performance for the detection of dopamine with a linear range from 1 ?M to 60?M and a limit of detection (LOD) as low as 0.02 ?M based on S/N = 3. In addition, this electrochemical sensor was applied to the simultaneous detection of dopamine and uric acid by using DPV with high sensitivity and selectivity.2. With the aid of PDDA, Pd and Pt ions can be assembled onto the surface of PDDA-GO, and subsequently both metal ions and GO can be simultaneously reduced to produce highly dispersed Pd-Pt nanoparticles onto RGO. The electrochemical behaviors of Pd-Pt/RGO/GC modified electrode towards dopamine (DA) and uric acid (UA) in the presence of high concentration of ascorbic acid have been investigated by DPV experiments. The results indicate that the electrochemical sensor exhibites improved sensitivity and selectivity. The electrochemical oxidation signals of AA, DA and UA are well separated into three distinct peaks with peak potential seperations of 0.176 V,0.194 V and 0.370 V between AA-DA, DA-UA and AA-UA respectively in DPV studies. The calibration curves for DA and UA were obtained in the range of 1?10 ?M (r= 0.997) and 50?300 ?M (r= 0.999), respectively.