The Preparation Of Carbon Dots And Graphene Composite Materials And Their Applications In The Bioelectrochemistry Sensor

Nano carbon materials because of its unique electrical, optical and mechanical properties, have potential value and broad application prospect in many areas, and research of nanometer carbon composite material is the best means to achieve its potential application value.In this paper, based on the special properties of large surface area, high catalytic efficiency and multiple active sites of carbon dots, carbon dots-based composite modified electrodes were prepared.Graphene has good conductivity,mechanical strength, high specific surface area and so on superior features and can quickly homogeneous transmission electron, graphene-based composite modified electrodes were prepared, carbon dots-based composite and graphene-based composite were used for the determination of dopamine and uric acid. Some novel electrochemical sensors for assaying of biological micromolecules dopamine and uric acid were constructed. The main contents are as follows:(1) In this study, we developed and characterized a new dopamine sensor based on the reduced graphene oxide-carbon dot composite film with high sensitivity and good stability. The carbon dots had carboxyl groups with negative charge, which not only provided good stability, but also enabled interaction with amine functional groups in DA through electrostatic interaction to enhance the specificity of DA with high specificity, and the interaction and electron communication between rGO and DA can be further strengthened via π-π stacking force. A linear relationship between the oxidation peak current of DA and its concentration could be obtained in a range from 0.01-450 μM with the limit of detection as 1.5 nM (3S/N). Furthermore, rGO-CDs/GCE exhibited good ability to suppress the background current from large excess ascorbic acid and uric acid. Meanwhile, the rGO-CDs/GCE also was applied to the detection of DA content in the injection of DA with satisfactory results, and the biosensor could keep its activity for at least six weeks.(2) In this study, a simple and convenient method for the synthesis of nitrogen-doped carbon dots was reported. N-CDs and ferrocene@β-cyclodextrin (Fc@β-CD/N-CDs)composite film modified glassy carbon electrode was prepared. The morphology and performance of Fc@β-CD/N-CDs was characterized by Transmission electron microscope, UV-vis absorption spectra,fluorescence spectra and FT-IR spectra. Layers of N-CDs and ferrocene@β-cyclodextrin host-guest complex were stacked on a glassy carbon electrodewhich was then used to study the electrochemistry of UA in pH 4.0 solution. The Fc@(3-CD/N-CDs showed that it was better electrochemical response for the detection of UA than that of GCE、N-CDs/GCE and Fc@β-CD/GCE.Differential pulse voltammetry gives a peak whose intensity is linearly related to the concentration of uric acid in the range from 5-120 μM, and the detection limit is 0.08 μM (S/N=3). The modified GCE showed good selectivity and sensitivity for uric acid and was applied to determine uric acid in spiked samples with satisfactory results.(3) Generally, synthesis of bimetallic nanoalloys requires utilization of surfactants or polymers to control its morphology and size. Under this circumstance, the insufficient interfacial contact between the organic ligands stabilized metal particles and supports, thus could hinder efficient charge carriers transfer. Herein, we report a facile, one-pot in situ synthesis of bimetallic Au-Pd nanoalloys on the surface of graphene oxide in aqueous phase. This sample is labeled as Au-Pd-rGO. The functional group of graphene oxide surface as surfactants could effectively promote formation and loading of Au-Pd nanoalloys onto the reduced graphene oxide. Au-Pd-rGO was dispersed in Nafion ethanol solution for electrochemical selectivity determination of dopamine. The Au-Pd bimetallic nanoalloys showed more excellent electrochemical performance than Au or Pd monometallic nanoparticles. The Au-Pd-rGO/NF modified electrode exhibited superb electrocatalytic activity towards the oxidation of DA with good sensitivity, wide linear range (0.02-200 μM) and low detection limit (2.35 nM). The proposed method was successfully applied to the determination of DA in dopamine injection with satisfactory results.(4) Nafion covered core-shell structured Fe3O4@graphene nanospheres (GNs) modified glassy carbon electrode was successfully prepared and used in the selective detection of dopamine. Firstly, the core-shell structured Fe3O4@GNs was synthesized by one-step chemical hydro-thermal synthesis reaction, and characterized by scanning electron microscopy, transmission electron microscopy and Raman spectroscopy.Then the Nafion cover core-shell structured Fe3O4@GNs was performed and further applied in the determination of DA in the presence of AA and UA, and the results showed that the coexisted AA and UA had no interference toward the electrochemistry of DA. The oxidation peak current (Ipa) of DA was linear with the concentration of DA in the range from 0.02-130 μM with the limit of detection as 0.007 μM (3S/N). Furthermore, the core-shell structured Fe3O4@GNs/Nafion/GCE was applied to the detection of DA content in real samples and satisfactory results were got, indicating a bright future of this material in biosensor applications.