Preparation Of Tryptophan-functionalized Graphene And The Electrochemical Sensor Research

Graphene(GR) is two-dimensional nanomaterial consisting of a single layer of sp~2 network of carbon atoms. It is an ideal material for electrochemistry because of its very high conductivity, large surface area and low cost. However, graphene is hydrophobic and has poor dispersion in the solution. Its strong tendency to form agglomerate irreversibly or even restack to form graphite through van der Waals interactions and strong π-π stacking, which limits its further application. Functionalized the graphene, improved the dispersion of graphene in solution, is the main method for graphene application at present.In this dissertation, basised on the characteristics of graphene, we focused on the functionalized graphene was synthesized by the noncovalent π-π conjugate action between graphene and tryptophan molecule to improved its dispersibility and electrocatalytic activity. The tryptophan functionalized graphene modified electrodes was prepared and used to simultaneous determination of ascorbic acid, dopamine and uric acid. Then electrochemical depositing AuNPs onto the surface of tryptophan functionalized graphene, based on the synergistic effect of Trp-GR and AuNPs further improved the electrocatalytic activity toward sensitive detection of dopamine. The main contents are described as follows: 1. Simultaneous determination of ascorbic acid, dopamine and uric acid based on tryptophan functionalized grapheneA new type of Tryptophan-functionalized graphene nanocomposite(Trp-GR) was synthesized by utilizing a facile ultrasonic method via π-π conjugate action between graphene(GR) and tryptophan(Trp) molecule. The material as prepared had well dispersivity in water and better conductivity than pure GR. The surface morphology of Trp-GR was characterized by scanning electron microscopy(SEM), transmission electron microscopy(TEM) and Raman spectroscopy. The electrochemical behaviors of ascorbic acid(AA), dopamine(DA), and uric acid(UA) were investigated by cyclic voltammetry(CV) on the surface of Trp-GR. The separation of the oxidation peak potentials for AA-DA, DA-UA and UA-AA was about 182 mV, 125 mV and 307 mV, which allowed simultaneously determining AA, DA, and UA. Differential pulse voltammetery(DPV) was used for the determination of AA, DA, and UA in their mixture. Under the optimum conditions, the linear response ranges for the determination of AA, DA, and UA were 0.2-12.9 mM, 0.5-110 μM, and 10-1000 μM, with the detection limits(S/N = 3) of 10.09 μM, 0.29 μM and 1.24 μM, respectively. Furthermore, the modified electrode was investigated for real sample analysis. 2. Au nanoparticles on tryptophan functionalized graphene for sensitive detection of dopamineA novel and uniform gold nanoparticles / tryptophan functionalized graphene nanocomposite(AuNPs/Trp-GR) has been successfully fabricated by directly electrochemical depositing gold onto the surface of tryptophan functionalized graphene(Trp-GR). The nanostructure of AuNPs/Trp-GR was characterized by using the scanning electron microscopy(SEM) and energy dispersive X-ray spectroscopy(EDS). It was demonstrated that Au nanoparticles were well dispersed on the surface of Trp-GR which might attribute to the more binding sites provided by Trp-GR for the formation of Au nanoparticles. The electrocatalytic activity of the AuNPs/Trp-GR towards the dopamine(DA) was systematically investigated using cyclic vo ltammetry(CV) and differential pulse voltammetry(DPV). Under optimum conditions, a wide and valuable linear range(0.5–411 μM), a low detection limit(0.056 μM), and good repeatability and stability were obtained for the determination of DA. Furthermore, the modified electrode was successfully applied to real samples analysis.