Construction And Electrochemical Performance Of Flexible Glucose Sensor Based On Carbon Fiber Membrane

Glucose is the most basic energy source for human cells and tissues,is also the main intermediate product in the body’s metabolic process.High glucose concentration in human body can lead to diabetes,which seriously threaten human health and life.The monitoring of blood glucose index plays an important role in the prevention,diagnosis and treatment of diabetes.Glucose electrochemical sensor has attracted more and more attention of researchers because of its advantages of fast,accurate,simple operation and high economic efficiency.Induction electrode,the core component of electrochemical sensor,is composed of substrate electrode and active substance.The application of traditional rigid electrode is limited due to its simple surface structure,high fabrication cost and instability.In this paper,the flexible electrode was used as the starting point to study the construction and electrochemical performance of glucose electrochemical sensors.The flexible carbon nanofibers with self-supporting structure were prepared by simple spinning process and heat treatment process using polyacrylonitrile as carbon source.The transformation of morphology and structure of the fibers during heat treatment was studied.After heat treatment,the surface of polyacrylonitrile nanofibers crumpled,the diameter became thin and the texture became fragile.The molecular groups of the fibers undergone cyclization reaction during the pre-oxidation process;The crystallization peak at 2θ=17.2°gradually disappeared,and the intensity of the（002）diffraction peak near 2θ=25.9°gradually increased,and the internal structure changed,and the fibers were gradually transformed into graphite carbon.The carbonization process was accompanied by complex chemical reactions such as fibers oxidation、dehydrogenation and intermolecular cross-linking,in which non-carbon elements were removed and carbon elements were enriched.The apparent crystallinity of carbon nanofibers increased and the internal structure of carbon nanofibers became orderly.Subsequently,carbon nanofibers were used as flexible substrate electrode and chitosan was used as carrier material of glucose oxidase to construct enzyme glucose sensor.The linear range of the electrodes were 6.5-14.5 mmol/L and 19.5-50.5 mmol/L,and the corresponding sensitivities were 1.80μAmmol/L^-1cm^-2（R²=98.8%）and 4.87μAmmol/L^-1cm^-2（R²=98.5%）,respectively.The minimum detection limit was 18.5μmol/L（S/N=3）.The Michaelic-Menten constant was 12.35 mmol/L,and the affinity between glucose oxidase and carbon nanofibers was strong.The enzyme electrode had good anti-interference,stability and repeatability.Carbon nanofibers and chitosan had excellent biocompatibility and stability,providing a biological microenvironment for enzyme to maintain their catalytic activity.As biological protein macromolecules,enzyme their catalytic activity will be affected by environmental factors（p H,temperature,etc.）.To improve the stability of the sensor,the fourth generation nonenzyme glucose sensor electrode was constructed by using potentiostatic deposition technology to modify platinum nanosheets directly on the conductive carbon nanofibers.Combining the advantages of flexible electrodes and enzyme-free sensors,the electrode had a wide linear range（7.5-87.5 mmol/L）and a low detection limit（14.04μmol/L）.The electrode had good repeatability,stability and strong anti-interference ability.Potentiostatic deposition technology had the advantages of low cost,simple preparation process and without binder,which greatly improved the electrical conductivity of the electrode.Carbon nanofibers maintained complete fiber morphology and provided a continuous one-dimensional conductive channel for electron transport.The platinum nanosheets deposited on the electrode were firmly bound to the carbon nanofibers.The large specific surface area and good catalytic ability accelerated the diffusion rate and catalytic efficiency of glucose on the electrode surface.