Preparation Of Functionalized Graphene Nanocomposites And Its Application On Electrochemical Sensors

Ever since the ?rst isolation of free-standing graphene sheets in year 2004,graphene has already demonstrated great potentials in various novel sensors which utilize its pluripotent sensing capabilities, such as exceptional electrical properties(e.g., extremely high carrier mobility and capacity), electrochemical properties(e.g.,high electron transfer rate), structural properties(e.g., one-atom thickness and extremely high surface-to-volume ratio), and its mechanical properties(e.g.,outstanding robustness and ?exibility). In order to enhance its sensitivity, speci?city,loading capacity, biocompatibility, etc, it is often necessary to functionalize it with recognition elements that bring the detection targets onto the graphene surface through speci?c interactions and sometimes also assist in signal transduction.In this thesis, we laid our emphasis on the fabrication of some functionalized graphene nanocomposites utilizing simple and novel methods and studying their applications in electrochemical sensors. The main contents are as follows:1. We demonstrate that Au-graphene/PDDA nanocomposites(Au-G/PDDA) can be rapidly synthesized through a facile, cost-effective, one-pot method with the use of poly(diallydimethylammonium chloride)(PDDA) as both reducing and stabilizing agents. The prepared Au-G/PDDA nanocomposites film endowed the modi?ed electrode high electron transfer rate and excellent electrocatalytic activity toward nitrite oxidation. Under the optimal conditions, the oxidation current increased linearly with increasing the concentration of nitrite in the range of 0.05-8.5 μM and the detection limit of 0.04μM at a ratio of signal to noise of 3.2. A facile method was developed for synthesis of molecularly imprinted polymer(MIP) nanomaterial based on self-polymerization of dopamine(DA) on the surface of reduced graphene oxide(RGO) in the presence of template cefotaxime(CEF). Thus, this approach to MIP sensors can enable the rebind of a speci?c template to be increased to achieve improved sensor capacity. The applicability of the presented sensor has been applied to the determination of CEF in real samples with satisfactory results.3. A rapid, environmental friendly, and sensitive sensor for the detection of bisphenol A(BPA) was developed at glassy carbon electrode(GCE) modified with Tannic acid functionalized N-doped graphene(TA/N-G) immobilized by Nafion.Compared with other sensors, the proposed sensor greatly enhanced the response signal of BPA due to the active surface area of N-G and high absorption efficiency of TA. Under the optimal conditions, the oxidation current increased linearly with increasing the concentration of BPA in the range of 0.05- 13 μM with the detection limit of 4.0 nM. The fabricated electrode showed good reproducibility, stability and anti-interference. The developed electrochemical sensor was successfully applied to determine BPA in food package.4. One-pot synthesis of CuS nanoparticle-decorated reduced graphene oxide(CuS/rGO) nanocomposites was prepared with the use of L-cysteine, an amino acid,as a reducing agent, sulfur source, and linker to anchor CuS nanoparticles onto the surface of rGO sheets. The synthesized materials were characterized with different methods such as scanning electron microscopy(SEM), and cyclic voltammetry.Furthermore, the electrocatalytic effect of the nanohybrid was investigated in the reduction of hydrogen peroxide and the oxidation of glucose. It was found that the CuS nanoparticles decorated reduced graphene exhibit a remarkable catalytic performance for glucose oxidation. The proposed sensor also showed high anti-interference ability, excellent selectivity and was successfully used for glucose detecting in human serum with good accuracy and satisfactory recovery. It is believed that CuS/RGO composites show good promise for further application on non-enzymatic glucose biosensors.5. A novel electro-active material was successfully prepared with ferricyanide ions loaded by electrostatic interaction onto the layer of prepared RCO-PDDA.Further, an electrochemical sensor for use in ascorbic acid(AA) detection was constructed with the use of the above electro-active materials RCO-ferricyanide/PDDA matrix as an electron mediator. The electrocatalytic oxidation of AA by ferricyanide was observed at the potential of 0.08 V, which was negative shift compared with that by direct electrochemical oxidation of AA on a glassy carbon electrode. The experimental parameters, including the pH value of testing solution and the applied potential for detection of AA, were optimized. The current electrochemical sensor not only exhibited a good reproducibility and storage stability, but also showed a fast amperometric response to AA.