The Preparation Of Graphene And Its Composite Modified Electrodes And Their Applications In Electrochemical Sensors

The electrochemical sensor is an important branch of sensor due to good selectivity, high sensitivity, simple equipment, low cost and easy miniaturization. Combined with materials science, biology and medicine, the electrochemical sensor has become one of the more active fields of contemporary analytical science, which is widely used in industry, environmental protection, food, drugs and agricultural analysis and so on. Graphene, a flat monolayer of carbon atoms tightly packed into a two-dimensional honeycomb lattice, has attracted widespread attention recently due to its high surface area, unique electronic transport property,high electrocatalytic activity and good chemical stability. Owing to its unique properties, graphene can greatly improve the performance of chemical sensor.In this paper, we prepared the graphene-based nanocomposites by simple and novel methods and employed them to fabricate new sensors, which were applied to the detection of some biological small molecules, environmental pollutants and food additives. The developed sensors showed high sensitivity, good selectivity and low detection limit, and were successfully applied for the determination of real samples. The main contents of this paper include:(1) The preparation of hollow gold nanoparticles-graphene composites and their application in the detection of dopamineGraphene is an ideal material for fabricating novel electrochemical sensors. However, these applications are limited because of the aggregation of graphene sheets through strong π-π stacking interaction and van der Waals interactions in aqueous solutions. With the appropriate surface treatment or surface functionalization, not only the agglomeration of graphene sheets can be prevented, but also some functionalized graphene nanocomposites can be fabricated.Firstly, the well-dispersed PVP-functionalized graphene was prepared with hydrazine as reductant in aqueous solution. And then, the hollow gold-graphene (HAu-G) nanocomposites can be simply prepared by mixing hollow Au nanoparticles solution with PVP-functionalized graphene dispersion. The morphologies and structures of the as-prepared nanocomposites were characterized by TEM and XRD, and the electrochemical behavior of the nanocomposites was characterized by EIS. The results exhibit that a large number of hollow gold nanoparticles with uniform morphology were loaded on graphene sheets and the HAu-G shows high surface area, unique electronic transport property. Furthermore, we found that the HAu-G modified glassy carbon electrode (HAu-G/GCE) exhibited greatly enhanced electrocatalytic activity towards the oxidation of dopamine (DA). Amperometric detection of DA at the HAu-G/GCE presents a wider linear range (0.08～600μM) and a lower detection limit (0.05μM). The results of differential pulse voltammetry show that the interference of AA and UA is entirely eliminated in the determination of DA in PBS (pH 6.0). The HAu-G/GCE is employed to determine the dopamine in injection and the satisfying results are achieved.(2) Application of poly(4-aminobenzoic acid)/graphene composite films in acetaminophen electrochemical sensorElectrochemical reduction of graphene oxide to graphene has recently attracted more interests due to its fast and green nature. The properties of the ERGO can be tuned by controlling the electrolysis parameters. Especially electrochemical approach may produce graphene directly onto the electrode substrates which could be used for specific applications, such as electrochemical sensor and biosensor without further steps or treatments.We have fabricated poly(4-aminobenzoic acid)/electrochemically reduced graphene oxide composite film modified glassy carbon electrodes (4-ABA/ERGO/GCEs) by a two-step electrochemical method. Electrochemical behavior and voltammetric determination of acetaminophen at the 4-ABA/ERGO/GCE was investigated in detail. The results show that the 4-ABA/ERGO/GCE exhibits an excellent electrocatalytic activity towards the oxidation of acetaminophen. The electrochemical reaction of acetaminophen at 4-ABA/ERGO/GCE is proved to be a surface-controlled process involving the same number of protons and electrons. The voltammetric determination of acetaminophen performed with the 4-ABA/ERGO modified electrode presents a good linearity in the range of 0.1～65μM with a low detection limit of 0.01μM. In the case of using the 4-ABA/ERGO/GCE, acetaminophen and dopamine can be simultaneously determined without mutual interference. Furthermore, the 4-ABA/ERGO/GCE has good reproducibility and stability, and can be used to determine acetaminophen in tablets.(3) Electrochemical behavior and voltammetric determination of p-nitrophenol based on electrochemically reduced graphene oxide modified electrodep-nitrophenol (p-NP) is widely used as intermediates in the production of pharmaceuticals, dyestuffs and pesticides. In addition, p-NP can also be used as leather fungicide and acid-base indicator. Therefore, p-NP will be inevitably released into environment to cause pollution during its production and application for agriculture and industry. Owing to it extreme toxicity on humans, animals and plants and difficult to degrade through the conventional treatment process, p-NP is considered to be a priority toxic pollutant by US Environmental Protection Agency. Therefore, it is very urgent and important to develop simple and reliable method for determination of trace amounts of p-NP in environment.The graphene modified glassy carbon electrode was prepared by one-step electrochemical reduction method. The modification process is fast and simple. The electrochemical behavior of p-NP at the modified electrode was investigated by means of cyclic voltammetry. Compared to that at a bare GCE and graphene oxide modified electrode, the reduction peak current of p-NP at the graphene modified electrode is significantly increased. This can be attributed to high surface area, good conductivity and strong adsorption ability of the graphene. The modified electrode was applied in a sensor for highly sensitive voltammetric determination of p-NP. Under optimal conditions, the sensor exhibits excellent performance for detecting p-NP with a good linearity in the range of 0.12～12μM and a low detection limit of 0.14μM. Furthermore, the electrode has good reproducibility and stability, and would be applied to the determination of p-NP in environmental pollutants.(4) Highly sensitive detection of tert-butylhydroquinone using graphene-carbon nanotubes modified electrodeOils and fats foods are essential in our diet, but such foods tend to oxidation and rancidity, which seriously affect the quality of the food, and may even be harmful to our health. In order to prolong the induction period of food oxidation, improve the stability of food, and then extend the shelf-life of foodstuffs, antioxidants are broadly used in the food industry. Among the most common antioxidants are phenolic compounds, especially tert-butylhydroquinone (TBHQ), which are frequently used to prevent oxidative degradation of oils and fats. Though TBHQ has widely used, potential risk that may lead to food safety problems cannot be ignored.Graphene-multi-walled carbon nanotubes (G-MWCNTs) nanocomposites were synthesized via reduction of hydrazine. The morphologies and structures of the as-prepared nanocomposites were characterized by TEM, XRD and Raman spectra. The electrochemical behaviors of TBHQ at G-MWCNTs modified GCE were investigated with cyclic voltammetry. The results indicated that the G-MWCNTs/GCE showed high electrocatalytic activity to the oxidation of TBHQ. The electrode was used for the detection of TBHQ through chronoamperometry. Under optimized conditions, this electrode presents a linear response in a broad concentration range of 0.25～900μM of TBHQ, with its detection limit reaching 0.15 μM. The excellent performance is attributed to the synergistic effects between graphene and carbon nanotubes. We have also demonstrated that the sensing performance is highly reproducible and stable, and afterwards it is applied for TBHQ detection in real food samples, including oils and beverages.