| According to the participation of enzymes in the process of glucose oxidation,glucose sensors are classified into two types:enzyme glucose sensor and enzyme-free glucose sensor.Due to instability,high cost and difficulty in immobilization of the enzyme,the application of enzyme-free glucose sensors is limited in many cases.Therefore,many researchers focus on the fabrication of enzyme-free glucose sensors.Developing an enzyme-free glucose sensor with high performance and low cost has become a hotspot in recent years.Nickel foam(NF)is a porous 3D material with a large surface area.Therefore,molecules or ions in a solution are easy to pass through the pores,and arrive at or leave from the solid-liquid interface.On the other hand,there are many high active Ni(OH)2/NiOOH redox couples near the interface.Therefore,NF has been widely used as an electrode material for glucose-free enzyme sensors.However,it is well known that the biocompatibility and chemical stability of NF are not ideal.Some functional materials are needed to modify the NF surface to improve the performance on glucose sensing.Among the materials,nickel cobalt oxide(NiCo2O4)presents a good biocompatibility and biological activity.After Ni atoms are bound to C03O4,the product NiCo2O4 can provides more catalytically active sites and many effective electrolyte-accessible ion transport channels.Therefore,NiCo2O4 modified NF is supposed to be able to enhance the performance on glucose detection.Herein,pieces of NF were used as the matrix material for fabricating NF/NiCo2O4 nanocomposite through a hydrothermal method following a calcination technology,namely "two-step" method.The nanocomposite then was characterized by several experimental methods,including scanning electron microscopy,inductively coupled plasma optical emission spectrometer,transmission electron microscopy,Xray diffraction and fourier transform infrared spectroscopy,etc.The electrocatalytic property of NF/NiCo2O4 to glucose oxidation was also studied in an alkaline medium.Further,polypyrrole(Ppy)was coated on the surface of NF/NiCo2O4 nanocomposite by an oxidant-induced in-situ polymerization method.Based on the NF/NiCo2O4@Ppy hybrid,we fabricated an enzyme-free electrochemical glucose sensing electrode based,along with characteristics related to the electrode.Several electrochemical methods(cyclic voltammetry,i-t curve,impedance spectroscopy and tafel plot)were employed to study the performance of NF/NiCo2O4@Ppy electrode on electrocatalyzing glucose oxidation in sodium hydroxide,as well as its selectivity,stability and reproducibility.The results indicate that core-shell NiCo2O4@Ppy nanowires are successfully synthesized on the surface of NF.The fabricated NF/NiCo2O4@Ppy sensing electrode shows an excellent electrocatalytic activity for glucose oxidation in an alkaline medium due to the synergy among the 3D structure of NF,the core of NiCo2O4 and the conductive outer shell of Ppy.In glucose sensing,tested concentration range was divided into three linear segments,1.0μmol/L-0.10 mmol/L,0.10-2.0 mmol/L and 2.0-20.0 mmol/L,respectively.The detection sensitivity can reach as high as 3059 μA/(mmol/L cm2),and the detection limit can be as low as 0.22 μmol/L(S/N=3).Anti-interference test results show that the current responds to dopamine,ascorbic acid,lactose,sucrose,fructose and NaCl are only 0.5-1.5%of the glucose response current.In addition,the fabricated sensing electrode exhibits a good reproducibility(RSD=1.28%)and stability.After 30 days,the response current remains at around 95%of the initial response current. |
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