Preparation Of PANI@Ni（OH）₂/NF For Non-Enzymatic Lucose Sensing And A Semi-Empirical Method To Fit Current-Concentration Curve

The common glucose sensors are divided into enzymatic glucose sensors and non-enzymatic glucose sensors（NEGSs）.For an enzymatic glucose sensor,the enzyme activity is easily affected by environmental factors,such as temperature,pH,and so on.Therefore,the research and application of NEGSs have attracted wide attention near decades.Nickel foam（NF）,an excellent substrate with a honeycomb 3D structure and plentiful active sites,has widely used as substrate material for electrochemical sensors.It is generally acknowledged that Ni（OH）₂/NiOOH redox couple co-exists in an alkaline solution when a Ni-based electroactive material is applied to detecting glucose.Then Ni（Ⅲ）oxidizes glucose to glucolactone,causing changes in current.Compared with Ni and NiO,Ni（OH）₂ is more beneficial to improve the sensitivity of NEGS.However,Ni（OH）₂ is a poor conductor and easy to leave electrode region by diffusion.It is necessary to modify the surface with some conductive material,such as conductive polymers.Polyaniline（PANI）,a famous conductive polymer,exhibits many advantages,such as large surface area,good biocompatibility and excellent chemical stability.Therefore,polyaniline can be used as a modified material for Ni series glucose sensors to improve their charge transfer ability and stability.In this paper,the surface of nickel foam was hydroxylated under alkaline conditions to form Ni（OH）₂/NF electrode.And then polyaniline nanofilm successfully coated on Ni（OH）₂/NF electrode surface by in-situ polymerization,marked as PANI@Ni（OH）₂/NF.The electrode materials were characterized by SEM,XRD,FT-IR and XPS.Cyclic voltammetry was utilized to study the electrochemical performance of PANI@Ni（OH）₂/NF composite electrode in 0.1 mol/L NaOH,as well as the selectivity,reproducibility and stability.In addition,chronoamperometry was used to study the current-time curve of PANI@Ni（OH）₂/NF in alkaline solution with successive addition of glucose.According to diffusion coefficient of glucose in the alkaline solution and the formula of Cottrell,we do nonlinear fitting between the response current（i）and the concentration of glucose（c）,making the relationship between the current response and glucose levels more accurately.The experimental results show that the as-fabricated PANI@Ni（OH）₂/NF sensor presents a rapidly current response about 3 s to the change of glucose concentration in a wide range glucose concentration of 1.0 μmol/L-16.0 mmol/L,as well as an excellent selectivity,longteam stability and reproducibility.The sensitivity can reach 1706.9 μA/（mmol/L cm²）and and the LOD is 0.46 μmol/L（S/N=3）,respectively.Therefore,PANI@Ni（OH）₂/NF can be used as an enzyme-free glucose biosensor,and its outstanding performance can be attributed to the hydroxylation of NF surface and the synergistic effect between PANI and Ni（OH）₂/NF.Electrochemical kinetics studies show that the reaction of sensing glucose on the surface of the PANI@Ni（OH）₂/NF electrode is a typical diffusion control process.According to Cottrell formula,within the whole range of glucose concentration,we successfully fitted the nonlinear semi-empirical equations of i and c:i=0.136*D^0.5*c^0.4Further research suggests that the semi-empirical equation can precisely express the relationship between i and c over a wide range of glucose concentration and eliminate the error caused by piecewise linear fitting method.