Non-enzymatic Glucose Sensor Based On Transition Metal Oxide Arrays

Diabetes is recognized as a kind of global health problem.Prompt and accurate detection of human blood glucose concentrations is an important way to control diabetes.Enzyme-based glucose sensors show high cost and poor stability.Therefore,people try to explore non-enzymatic sensor that can efficiently detect the glucose concentration without glucose oxidase,which mainly rely on the electrocatalytic oxidation of glucose by electrode active materials.Among them,transition metal oxides are a kind of popular electrode active materials,which not only show good electrocatalytic ability to glucose molecules,but also are abundant on the earth and cheap.However,they show poor electrical conductivity and most of the current studies focus on preparing powder material,which need to be fixed on the surface of the traditional electrode using additional conductive adhesive.This method will lead to the blockage of the active sites,which will damage the detection performance of the sensor.The performance of the non-enzymatic glucose sensor can be improved by using some methods,such as improving the electrical conductivity,adjusting the micromorphology,changing the electrode preparation method.In this work,simple hydrothermal method was used to in-situ form metal oxide array on the conductive substrate to construct three-dimensional（3D）self-supporting electrodes,and the classical electrochemical three-electrode system was used to study its non-enzymatic glucose sensing performance.The main content is as follows.（1）Porous Co₃O₄ nanowire arrays were synthesized on nickel foam（Co₃O₄NWs/NF）by one-step hydrothermal method.X-ray power diffraction（XRD）,scanning electron microscopy（SEM）and transmission electron microscopy（TEM）were used to characterize the composition and morphology of the products.Some electrochemical methods were used to investigate its non-enzymatic glucose sensing performance in alkaline solution.The results showed that the sensitivity of Co₃O₄ NWs/NF electrode to glucose was 4570μA m M^-1 cm^-2,the linear range was 1μM-0.337 m M,and the detection limit was 0.91μM（S/N=3）.It also showed good selectivity and repeatability.（2）To improve the electrical conductivity,porous NiCo₂O₄ nanowire arrays were prepared on nickel foam（Ni Co₂O₄ NWs/NF）by a simple hydrothermal method.Part of Co²⁺in Co₃O₄ was replaced by Ni²⁺to form bimetallic oxides Ni Co₂O₄ that exhibites better conductivity.XRD,SEM,TEM and energy dispersive spectroscopy（EDS）were used to verify the successfully synthesis of the 3D self-supporting electrode,and the non-enzymatic glucose sensing performance was tested by using a three-electrode system.This prepared electrode showed great electrocatalytic performance to glucose,with sensitivity of 5916μA m M^-1 cm^-2,wide linear range of 1μM-3.987 m M,detection limit of 0.94μM（S/N=3）.In addition,it showed rapid response time（about 3 s）,good selectivity and reproducibility.（3）In order to further meet the demand for high-performance non-enzymatic glucose sensor,it is necessary to carry out further optimal design of electrode active material,such as preparing material composites,controling morphology,etc.Hierarchical Co₃O₄/Ni Co₂O₄ composites were prepared on flexible carbon cloth（Co₃O₄/Ni Co₂O₄/CC）by a simple two-step method.ZIF-67 was utilized as precursor,which was grown in-situ on Ni Co₂O₄ nanowire arrays and transformed into porous Co₃O₄ hollow cube after annealing in the air.The composition and morphology of the products were characterized by XRD,SEM,TEM,EDS and X-ray photoelectron spectroscopy measurements（XPS）,which proved the successful synthesis of Co₃O₄/Ni Co₂O₄ composites with unique hierarchical structure.Then,the electrochemical method was used to investigate the performance of the non-enzymatic glucose sensor based on the fabricated electrode.The sensor exhibited excellent electrocatalytic performance,including an ultrahigh sensitivity of 12835μA m M^-1 cm^-2,a wide linear range of 1μM-1.127 m M,a low detection limit of 0.64μM（S/N=3）,and fast response time（～2 s）.It also delivered outstanding selectivity,repeatability and stability.