The Preparation Of Graphene And Its Application In The Electrochemical Detection Of Sialic Acid And Ovotransferrin

This paper prepared graphene from graphite powder, and comprehensively analysed their chemical structure and electrocatalytic activity. Analyse and compare the electrocatalytic activity of graphene prepared by vacuum drying and freeze-drying. The results found that the freeze dring graphene had a stronger electrocatalytic performance. Then the graphene was used as the amplified material of electrochem ical biosensor to construct specific biosensor, which were used to detect and analy-se sialic acid and ovotransferrin. The work is expected to provide the basic refere nee for the detection of the quality of hen eggs and their products.1. We used the modified Hummer’s method to prepare graphite oxide, according to the method of sonication, disperation, reduction, the used the ammonia water, which was less toxity and could stable the graphene suspension, as the reductant agent to prepare graphene with well water solubility and high specific surface area. Then we characterized the samples by UV-vis, Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), Zeta potential, scanning electron microscope (SEM), transmission electron microscopy (TEM). We found the differences between two samples with different drying method in microstructure and physical properties. The the electron microscopy found that the structure of the freeze drying graphene was loosing, and more porous. The changes in the oxygen-containing functional groups by FTIR showed successful preparation of graphene oxide(GO) and graphene. The characteristic peak at 11 c disappeared, and a peak appeared at 24° via XRD. This confirmed that the formation of graphene from graphene oxide required 15 h of reaction time. The value of the zeta potential of graphene prepared by freeze drying was about -32.6 mV, while graphene by vacuum drying was -21.6 mV. The results suggested that an aqueous solution of freeze-dried graphene has stronger disperation and stability.2. Due to the different morphology and structure of two graphene samples, we further characterize the samples through a series of methods, such as Roman spectra, X-ray photoelectron spectroscopy (XPS), BET specific surface area. Their conductive and electrocatalytic activityies were analysed through the cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), rotating disk electrode (RDE) and oxygen reduction reaction (ORR) voltammogram. The results of XPS revealed the freeze dry graphene contained more nitrogen, less oxygen, indicating the more complete reduction of freeze drying graphene, this finding echoes with the result of Raman spectra. The BET surface area of vacuum dry graphene and freeze dry graphene were 473.8 and 558.4 m2/g respectively. The conductivity of freeze drying graphene was 576 S/m, higher than the vaccum drying graphene 534 S/m. The peak currents of graphene-modified glass carbon electrode samples prepared by these two methods of drying were 83.95 μA and 59.6μA, respectively; the nearly vanished semicircle in electrochemical impedance spectroscopy highlights that the graphene had excellent electrocatalytic ability. Rotating disk electrode results in systems of uric acid, it was more active towards the electrooxidation of uric acid. A steeper slope demonstrates better ORR activity. Above all, we found that the Gr2 had a relatively better capacity to promote charge transfer. Therefore we used the freeze drying method as the amplified material to detect the components in hen eggs.3. Based on the specific interaction between hemagglutinin and sialic acid.First we optmized the volume of graphene, then actived the carbonyl group on the surface of graphene modified electrode by EDC/NHS, immobilized the hemagglutinin on the electrode by covalent coupling, to construct hemagglutinin electrochemical biosensor. Due to the specific binding between sialic acid and hemagglutinin, we could perform analysis and detection through the change during the combination between the biosensor and sialic acid. The biosensor exhibits a linear range that spans 7 orders of magnitude (10-11-10-17 M) for sialic acid, with a detection limit as low as 0.837 aM for sialic acid. Also the linear correlation coeffecient was beyond 0.9, and the biosensor had strong anti-interference and good stability. The same concentration 10-9 mol/L) of glucose, cysteine, ascorbic acid had a small resistance, so anti-interference ability of the sensor was very strong. After stored at 4℃ for 15 days, the test standard deviation is 4.7%, which demonstrated the electrochemical biosensor had a good stability.4. This part we also used the Gr2 as the signal amplified material, the difference was adopted electrochemical reduction method to immobilize graphene on the bare GCE. Then similarly actived the carbonyl group on the surface of graphene modified electrode by EDC/NHS, covalently immoblized antibody of ovotranferrin on the surface of electrode, to build electrochemical immuosensor. Because of the specific binding between antibody and antigen, according to the electrochemical signal changes between immunosensor and ovotransferrin, we detected and analysed the target. Results demonstrated that the biosensor exhibits a linear range from 10-1-10-9 mg/mL for ovotransferrin detection, with a detection limit as low as 0.593 pg/mL. Also the linear correlation coeffecient was beyond 0.9973. and the biosensor had strong anti-interference for lysozyme, ovalbumin, glucose and cystein.and good stability. After stored 15 days at 4℃, the test standard deviation is 7.6%, which demonstrated the electrochemical biosensor had a good stability. Therefore, the biosensor could be considered to applied in the real samples.