Construction Of Transition Metal Nanobiomimetic Enzyme Based Electrochemical Sensor And Its Application In Wearable Body Fluid Detection

For the human body,biologically active small molecules such as glucose and vitamin C are closely related to the normal physiological metabolic activities of the body.If the concentration in the body is abnormal,it can cause related diseases such as diabetes and scurvy,which can seriously affect human health.Therefore,it is crucial to obtain accurate and timely information on the concentration of bioactive small molecules in body fluids.Electrochemical detection is one of the most promising detection tools,especially based on the advantages of rapid response and high selectivity of bioenzyme-based electrochemical sensors,which are widely used.However,the catalytic activity of biological enzymes is susceptible to environmental influences,expensive and requires complex immobilization steps,which seriously hinders the further development of enzyme-based sensors,and therefore bionanzyme-based electrochemical sensors are born.The detection performance of bionic enzyme-based sensors is mainly determined by the electrode materials.Existing studies mainly focus on nickel and cobalt transition metal-based nanobionic enzymes,focusing on solving the problems of poor electrical conductivity,weak intrinsic catalytic ability and low utilization of these materials themselves.Based on this,a series of transition metal（Ni,Co）-based nanobionic enzymes were prepared by functionalized design through morphology modulation,multi-component composite,interface optimization and heterojunction construction,and the composition,morphology and structure of the electrode materials were characterized and the electrochemical sensors were constructed to realize the electrochemical analysis and detection of bioactive small molecules and real samples.The mechanism of nanobionic enzymes catalyzing bioactive small molecules was also explored by combining various characterization techniques.The details of the study and the main results are as follows.（1）Enhancement of glucose detection performance using a carbon-coated NiCo alloy nanobionic enzyme.NiCo-MOF was synthesized by hydrothermal method,and NiCo@C composites with carbon uniformly coated NiCo alloy nanoparticles（NPs）were obtained by reduction and in situ carbonization of the precursors in N₂ atmosphere.In this process,the graphitized carbon can effectively hinder the aggregation of the nanoalloy particles and improve the electrical conductivity.The physical and chemical properties of NiCo@C,such as morphology,composition,surface elemental chemical state and electrocatalysis,were investigated by combining various characterization tools,and the mechanism of the composite electrocatalyst performance enhancement was also explored.The NiCo@C bionic enzyme electrochemical sensor has good detection performance due to the synergistic effect of its nanostructure,alloy,graphitized carbon,and the effect of binary Ni/C electrocatalyst on the direct electron transfer pathway.At optimal potential conditions（0.50 V）,the sensor exhibited a wide linear detection range（0.5μM to 4.38m M）,high sensitivity(265.53μA m M^-1 cm^-2),low limit of detection（LOD）（0.2μM）,and also good reproducibility and stability.the NiCo@C nanobiont enzyme-based sensor was applied to the determination of glucose in human serum samples.It indicates that it has a good application prospect in the actual sample detection of glucose.（2）Improved glucose detection performance using NiCo-NiCo O₂@C nanocage bionanase.The organic carbon source encapsulated Ni-Co PBA derivatives were used to prepare nanocomposites containing alloy/transition metal oxide/carbon encapsulation（NiCo-NiCo O₂@C）by direct carbonization and reduction in Ar atmosphere.The process formed carbon nanocarriers encapsulated around the alloy/transition metal oxide nanoparticles with nano-cage structure,good electrical conductivity and large specific surface area,which can provide more catalytically active sites,facilitate electron transfer and accelerate electrolyte diffusion.The above characteristics can improve the electrocatalytic performance for glucose.The NiCo-NiCo O₂@C modified electrode was used for glucose detection,which exhibited high sensitivity(340.4 and 56.1μA m M^-1 cm^-2),wide detection range（0.1μM-600μM and 0.9 m M-6.3 m M）,low LOD（0.03μM）and fast response rate（response time<5 s）,as well as good selectivity,reproducibility and stability.Meanwhile,the NiCo-NiCo O₂@C modified electrode can be used to detect glucose concentration in human serum samples,confirming the potential application of this nanobionic enzyme as a glucose sensing detection material.（3）Enhancement of wearable electrochemical sensor performance for vitamin C（ascorbic acid）detection using Ni₃N/Ni/N-rGO nanobionic enzyme.Composites with three-dimensional porous structures of nitrogen-doped reduced graphene oxide（Ni₃N/Ni/N-rGO）with surface-loaded Ni₃N/Ni heterojunctions were fabricated by ammonia nitridation.The doping of nitrogen atoms during nitridation can effectively modulate the charge distribution of the sp² carbon skeleton,induce the generation of structural defects and increase the electron transfer rate.The nanobionic enzymes with porous structures were successfully synthesized by controlling different GO contents,nitriding temperatures and calcination times,and a high-performance electrochemical sensing system was constructed.Combined with relevant electrochemical tests,it was shown that Ni₃N/Ni/N-rGO has large electrochemically active area and higher electrochemical sensing activity.In addition,the bionic enzyme is able to accelerate the vitamin C oxidation reaction process,attributed to the Ni₃N/Ni with vitamin C-like enzymatic activity,the excellent interfacial electron rate,and the high electrical conductivity of N-rGO.Density flooding theory（DFT）simulations were used to investigate the Gibbs free energy change in the catalytic vitamin C process and the reaction mechanism of the electrocatalytic oxidation of vitamin C.By integrating Ni₃N/Ni/N-rGO bionic enzyme electrodes,Bluetooth 5.0 hardware,smartphones and application-specific integrated circuits（ASICs）,a wearable electrochemical sensing system was customized for data collection and analysis of vitamin C content in human sweat,thus demonstrating the potential application of Ni₃N/Ni/N-rGO as an vitamin C sensing and detection material.（4）Enhancement of wearable electrochemical sensor performance for vitamin C detection using two-dimensional conductive Ni₃（HITP）₂-MOF nanobionic enzymes.Highly crystalline conductive Ni₃（HITP）₂ was synthesized by a solvothermal method for electrochemical detection of vitamin C.The material has many advantages such as large specific surface area,high electrical conductivity（39.84 S/cm）,and good stability.The two-dimensional conductive Ni₃（HITP）₂-MOF topology with isolated Ni-N₄ units in a stacked honeycomb lattice reduces the binding energy of the reactant intermediates,thus providing highly active catalytic sites for vitamin C oxidation.The units of the MOF topology（located in the stacked honeycomb lattice）facilitate the electron transfer for the vitamin C-catalyzed reaction.Ni₃（HITP）₂/screen-printed carbon electrode（SPCE）device can be used to detect vitamin C content in alkaline media,and electrochemical tests have shown good sensitivity,wide linear range and low detection limits,which are superior to previously reported electrochemical non-enzymatic vitamin C sensors based on MOFs and MOF derivatives.A portable electrochemical vitamin C detection system was customized for electrochemical data acquisition and analysis by integrating Ni₃（HITP）₂/SPCE（sensing element）,Bluetooth 5.0 hardware,smartphone,and ASIC.This portable vitamin C sensing system shows good electrochemical performance in alkaline conditions and is capable of quantitative detection of vitamin C in human sweat.