Direct Electrochemistry Of Biomass Porous Carbons-based Glucose Oxidase And Its Glucose Biosensor Application

Diabetes have become the top of the five chronic diseases worldwide,and there is no therepy to completely cure at present.Nowadays,the rapid and sensitive detection of glucose plays a critical role in diabetes prevention and treatment.Electrochemical biosensor has been recognized as a sensitive,rapid,inexpensive and reliable diagnostic method toward glucose detection.The design and fabrication of accurate glucose electrochemical biosensor is of great significance for the prevention,diagnosis and treatment of diabetes mellitus as well as for the fundamental research of bioelectrochemistry.Although glucose electrochemical biosensor has been developed and used in clinic diagnosis for more than half a century,the immobilization of glucose oxidase and the construction of sensitive,inexpensive and reliable electrode sensors are still very challenging.Glucose oxidase direct electrochemistry-based 3^rd generation could be less expensive,more sensitive,more rapid and more reliable for glucose detection.Regulating the surface structure of the electrode to shorten the electron transfer distance between the GOx and electrode surface is the key step to realize the direct electron transfer of the protein.Biomass-derived porous carbon nanomaterials have been widely used in several fields of energy,environment and catalysis due to their high biocompatibility,rich functional redox groups and talorable porous structures.In this thesis work,different biomass-derived porous carbon materials and their nanocomposites were prepared and applied to the GOx fixation and construction of electrochemical biosensors,and the electron transfer mechanisms on the enzyme-modified electrodes was discussed for scientific insights.The main research contents and results are as follows:1.In chapter 1,various electrochemical biosensors are briefly introduced including the development trend of glucose electrochemical biosensors,their challenges and difficulties in enzyme immobilization and electrode optimization are discussed in detail;the applications of porous carbon nanomaterials in immobilization enzymes and electrochemical sensors are surveyed in detail,and the application and development of alternative inexpensive and simple biomass carbon materials;lastly,the research purpose,research content and innovation of this paper are briefly introduced.2.In chapter 2,glucose oxidase(GOx)was fixed on two kinds of porous biomass carbon nanomaterials(PHPBCs and GDBCs)prepared from two kinds of passion fruit pericarp(golden peal and purple peal)by electrostatic adsorption and self-assembly,and the electrochemical glucose biosensors without electronic medium was prepared.The microstructure,specific surface area and pore size distribution of PHPBCs were characterized by electron microscope(FESEM)and N₂ adsorption/desorption isotherms.The results showed that PHPBCs had richer pore structures and larger specific surface area(565.63>362.49 m²g^-l(GDBCs)),which is helpful to the fixation of GOx and the rapid direct electrochemical reaction of GOx without electron medium used as electrode material for bioelectrochemical glucose sensor with the two segments of linear range(0.0001-0.82 m M and 0.82-3.82 m M),the detection limit of 0.02?M,and the highest sensitivity of 33.40?A m M^-l cm^-2.The sensor has good selectivity to glucose and can avoid other interferences.3.In chapter 3,the porous construction of mesoporous carbon nanofibers(BPCNFs)materials was realized by regulating pyrolysis temperature with bacterial cellulose as biomass source used for GOx fixation.Electrochemical cyclic voltammetric detection was carried out in N₂-saturated and air-saturated electrolytes.Through the observation of oxidation reduction peak current,it can be found that mesoporous BPCNFs have good fixed effects and can realize obvious direct electrochemical process for GOx,and the analysis of pore size adsorption/desorption curves of BET showed that the mesoporous ratio of BPCNFs was closely related to pyrolysis temperature.The electrochemical sensor based on GOx-BPCNFs has better detection effect on glucose.The minimum detection limit was as low as 0.023?M,the response time was 3.7 s,the Michele constant was 0.61 m M,the highest sensitivity was 111.14?A m M^-1 cm^-2,and it has good anti-interference ability.This chapter proves that through the regulation of pyrolysis temperature,the structure of porous materials can be optimized,and the adsorption or load of protein molecules can be effectively increased,so as to achieve rapid DET of GOx.4.In chapter 4,loofah sponge-derived three-dimensional graphene biomass carbon porous silk-ball-like Mo composites(LSGBC@PSB-Mo)were prepared by hydrothermal method and high temperature pyrolysis method.The physicochemical properties and electrochemical behaviors of LSGBC@PSB-Mo were compared by electron microscopic and electrochemical testing.The enzyme electrode system for immobilization of GOx with each synthetic material as carrier was constructed and used to determine the direct electrochemical properties of GOx on the modified electrode and to study the response of those electrode sensors to glucose.The results showed that GOx-LSGBC@PSB-Mo electrode with unique silk-ball-like sandwich structure had excellent electrochemical sensing performance,which can not only promote the DET between GOx and electrode surface,but also improve the fixed quantity of GOx.Under the optimum experimental conditions,the linear relationship between glucose concentration and the increment of response current in the range of 1?M-5.1 m M was good and the sensitivity was 106.46?A m M^-1 cm^-2,the detection limit was 0.15?M(S/N>3),the response time was 3.2 s,and the Michele constant was 0.17 m M.In addition,the GOx-LSGBC@PSB-Mo/GCE sensor prepared in this chapter has high sensitivity,good reproducibility,long-term stability and good selectivity to glucose.5.In chapter 5,the main work is the preparation of cape gooseberry-derived prussian blue-like nano-carbon felts(PBL-NFs)with a novel biomass source and their application in protein immobilization,direct electrochemistry and high sensitivity glucose biosensor.Firstly,Fe nanorods,prussian blue-like cubic(PBLC)and carbon felt nanocomposites(PBL-NFs),which were prepared by simple immersion method,solvothermal method and pyrolysis in inert atmosphere,respectively.Through the test of physicochemical and electrochemical properties,it is found that Fe nanorods have good conductivity but can not fix GOx,and the DET of GOx fixed on PBLC surface with good GOx fixation is not enough.Notably,PBL-NF has the advantages of both high efficient loading of GOx and electron super-electrode transfer channel(SETCs),which realizes the high sensitivity of glucose detection(124.56?A m M^-l cm^-2).This work provides an inexpensive and convenient design scheme for the construction of glucose sensing platform with high catalytic activity,and has a great application prospect in biomedical,sensing,clinical diagnosis and other fields.In brief,a variety of biomass carbon nanomaterials with different structures(honeycomb,fiber interlacing,hydrangea and cube carbon felt structure,etc.)and their composites were synthesized from several inexpensive biomass and even wastes materials to improve the electrocatalytic performance of enzyme electrodes,especially to realize the direct electrochemistry in sensing applications.This thesis provides new approaches to develop the new generation of glucose sensors from biomass carbon nanomaterials and their composites while shedding scientific lights on the behaviors and mechanisms of protein direct electrochemistry,thus holding great promise to use recycle sustainable materials for important biosensing applications.