Design,Synthesis And Biosensing Application Of Graphene-Based Multi-Composite Materials

Graphene-based multi-composite materials are widely used in energy storage,sensors,electronic devices,batteries and other fields because of the combination of advantages of graphene and other functional components.Through the modification of components such as inorganic materials,polymers and carbon materials,graphene-based multi-composite will be greatly improved in water solubility,biocompatibility and electron transfer efficiency.Therefore,the biosensor constructed with this kind of materials will enable the enzyme or protein immobilized on it to obtain high activity,so as to improve the signal response of the sensor and obtain excellent analytical performance.Based on the synergistic effect of graphene and other components,multi-composite graphene based composites with unique structure were constructed,and their biosensing applications were exploredThe second chapter focuses on the synthesis of graphene based binary composites by in-situ synthesis.Meso-cellular silicate foam（MCFs）modified reduced graphene oxide（MCFs@r GO）were synthesized and studied.An integrated composite of polyoxyethylene-polyoxypropylene-polyoxyethylene（P123）was used as modifier to synthetise P123-r GO.As the polymeric template for the fabrication of mesoporous silicate,modified P123 greatly improved the affinity between the nanosheet and the in situ formed MCFs,resulting in the formation of thin layers of MCFs on both sides of the r GO.Therefore,the MCFs@r GO exhibited a unique sandwich structure with an inner skeleton of r GO and two outer layers of MCFs.The outer modification by MCFs,with the presence of large mesopores,not only shifted the surface property of r GO from hydrophobic to hydrophilic,but also offered subsequent immobilized enzymes a favorable microenvironment to maintain their bioactivity.The results show that,MCFs@r GO can be evenly dispersed in water for a long time,which will be conducive to the adsorption of water-soluble substrates in biosensor applications.Meanwhile,the inner skeleton of r GO compensated for the weak conductivity of MCFs,providing a pathway for rapid electron transfer as a conductive framework.The MCFs@r GO modified glassy carbon electrode（GCE）showed rapid electron transfer.In order to study the application of composites in the field of biosensors,the immobilization of two typical redox proteins and enzymes,hemoglobin（Hb）and glucose oxidase（GOD）was explored.The results show that,due to the large pore size of the outer layer of MCFs@r GO,the material has good adsorption for the two redox proteins and enzymes with different structures.After the adsorption,some space is still reserved in the mesoporous,which is conducive to the transfer of substrate in sensing applications,showing the great potential of composite materials for the construction of biosensors.In chapter 3,the application performance of MCFs@r GO in biosensor was systematically investigated.The direct electrochemical properties,electrocatalytic properties and universality for enzyme-immobilization were systematically studied.The results showed that,direct electron transfer（DET）of all the four redox proteins and enzymes such as Hb,horseradish peroxidase（HRP）,GOD and cholesterol oxidase（Ch Ox）was realized on MCFs@r GO modified GCE despite the great difference between their structures.On this basis,Hb-MCFs@r GO/GCE and GOD-MCFs@r GO/GCE are selected to investigate the enhancement of MCFs@Rgo on the DET of redox proteins and enzymes.It was found that the DET signal obtained from Hb-MCFs@r GO/GCE was much larger than the sum of the signals from two components-based modified electrodes of Hb-P123-r GO/GCE and Hb-MCFs/GCE.A similar improvement in DET signal was also observed using GOD-MCFs@r GO/GCE.The significant enhancement of DET signals for both two protein electrodes can be ascribed to the synergistic effects generated from the integration of the two components,one of which enhances biocompatibility and one enhances conductivity.The bioelectrocatalytic performance of Hb and GOD electrodes was further investigated.As for Hb-MCFs@r GO/GCE,the electrode displayed excellent analytical performance for the detection of hydrogen peroxide（H₂O₂）,including good sensitivity of 0.25μAμmol^-1L cm^-2,a low detection limit of 63.6 nmol L^-1,based on S/N=3,and a low apparent Michaelis-Menten constant(K_M^app)of 49.05μmol L-1.GOD-MCFs@r GO/GCE also exhibited good analytical performance for the detection of glucose,with a wide linear range of 0.25-8.0 mmol L^-1.In addition,blood glucose detection in samples of human serum was successfully achieved using GOD-MCFs@r GO/GCE with a low quantification limit.In Chapter 4,a ternary graphene based composites Au nanoparticles-polymeric ionic liquids-reduced graphene oxide（Au NPs-PILs-r GO）were constructed by sequential assembly method.The differences of biosensing performance between materials prepared by sequential assembly method and blending method are explored.Using polymeric ionic liquids（PILs）as bridging agent,inorganic Au NPs were compounded with r GO.Firstly,PILs can modify the surface of r GO byπ-πinteraction.The surface hydrophilicity of the obtained PILs-r GO was greatly improved due to the polarity of PILs.Secondly,using the unique ion exchange ability of PILs,Au NPs were in situ reduced at the modified position of PILs,thereby obtaining+the ternary composite Au NPs-PILs-r GO.Further,utilizing the negative charge property of PILs,ACh E was immobilized on the surface of the modified GCE by electrostatic self-assembly to construct ACh E-Au NPs-PILs-r GO/CCE.This integrated composite material combines excellent conductivity of metal nanoparticles and graphene with the good biocompatibility of PILs,which is conducive to maintaining the biological activity of enzymes and improving the analytical and detection performance in biosensor applications.On the one hand,the immobilization of ACh E by electrostatic adsorption can reduce the loss of ACh E activity,and on the other hand,ACh E can be enriched near PILs.Since Au NPs are modified in situ on PILs,that is,ACh E will be loaded at the position between Au NPs and r GO.This is conducive to electron transfer between enzyme catalytic products and electrodes,thereby further improving the electrocatalytic performance.The results showed that the catalytic performance of ACh E-Au NPs-PILs-r GO/GCE for acetylthiocholine chloride（ATCl）is significantly better than that of each single component modified electrode and the modified electrode prepared by simple blending of components.It is proved that the ternary structure of the composite plays an important role in improving the bioelectrocatalytic performance of the ACh E.Based on this,ACh E-Au NPs-PILs-r GO modified electrode was used to detect O,O-dimethyl-O-2,2-dichlorovinylphosphate（DDVP）,a organophosphorus pesticide.The detection limit was as low as 0.043 ng L^-1,and a wide linear range of DDVP was obtained on the electrode.In Chapter 5,an integrated ternary composite multi-walled carbon nanotubes-bovine serum albumin-reduced graphene oxide（MWCNTs-BSA-r GO）was constructed by sequential assembly method.The electrochemical biosensing properties of composites were discussed,and the differences of sensing performance between materials prepared by sequential assembly method and blending method were explored.The material has a structure similar to that described in Chapter 4,which is connected by third-party component.In the preparation process,one-dimensional（1D）-two-dimensional（2D）composite MWCNTs-BSA-r GO was constructed by using BSA as a linker,which can interact with graphene and MWCNTs respectively.BSA-r GO nanocomposites were prepared using BSA as reducing agent.The hydrophobic surface of r GO was transformed into hydrophilic by in situ modification of BSA in the reduction process.At the same time,the stacking of graphene layers was prevented by the hydrophobic interaction between charged proteins.Subsequently,BSA molecules modified on r GO adsorbed MWCNTs through surface dehydration and non-polar region.Therefore,the MWCNTs were assembled on the surface of BSA-r GO to form MWCNTs-BSA-r GO.By covalent coupling,BSA molecules can locate ACh E to the connection point of MWCNTs and r GO.In this way the modified electrode ACh E-MWCNTs-BSA-r GO was prepared.The catalytic ability of immobilized ACh E towards ATCl on different component modified electrodes was compared.The results showed that the immobilized enzyme maintained biological activity and showed good catalytic performance on MWCNTs-BSA-r GO.Compared with the enzyme modified electrode prepared by simple blending of components,ACh E-MWCNTs-BSA-r GO/GCE exhibited better catalytic response.It can be proved that the localization of ACh E is of great significance to improve the biocatalytic activity of the modified electrode.This is because the unique 1D-2D structure of the composite can build efficient pathways for the transfer of electron and material around ACh E,which is conducive to the electron transfer between the hydrolysate and the electrode.On this basis,the modified electrode was further used to detect organophosphoruspesticides.Theresultsshowedthat ACh E-MWCNTs-BSA-r GO/GCE has a wide linear range and low detection limit for the detection of DDVP.In addition,the modified electrode was also applied to the detection of real samples,and reliable results were obtained.