Biomimetic Catalysis Of Carbon-Based Nanozymes And Visible Detection In Food Analysis

Carbon-based nanozymes are a new category of nanomaterials with enzyme-like catalytic activity,which have significant advantages such as easy storage,adjustable performance,low cost,recyclability,and high stability.However,the catalytic activity of the most carbon-based nanozymes is still relatively low compared to that of natural enzymes,so further exploration of efficient synthetic processes is needed to improve their catalytic performance.Therefore,the current thesis is focused on how to improve the enzyme-like catalytic activity of carbon-based nanozymes and their applications.Three new carbon-based nanozymes with mimetic peroxidase activity were designed through high-temperature pyrolysis,phosphorus atom doping,template-assisted and gold nanoparticle loading strategies,and their morphological structure,catalytic mechanism and kinetics of enzymatic reactions were investigated.Finally,a colorimetric sensing platform was used to analyze total antioxidant capacity（TAC）,acetylcholinesterase activity,methyl paraoxon and Cr（VI）,breaking the limitations of traditional detection methods.It is expected to provide a theoretical reference for the design and synthesis of high-performance carbon-based nanozyme and the construction of highly sensitive sensors.The main research contents and results are as follows:（1）The metal-organic framework（MOF）was employes as a precursor for the preparation of iron/nitrogen-doped porous carbon-based nanozymes（Fe-N/C）with dodecahedral morphology and abundant metal active sites by high-temperature pyrolysis strategy.The Fe-N/C prepared enzymes maintain high peroxidase catalytic performance over a wide temperature and p H range,and exhibit excellent stability in repeated use,overcoming the shortcomings of natural enzymes which are prone to deactivation and cannot be recycled.Kinetic experiments verified that it has a catalytic activity comparable to that of horse radish peroxidase（HRP）.Furthermore,as the addition of antioxidants to the system competitively depletes the free radicals in solution and inhibits the formation of oxidation products,leading to a decrease in absorbance.Thus,an ultra-sensitive detection of antioxidants by monitoring the change in absorbance signal was designed and successfully applied it to the determination of TAC in fruit juice,kiwifruit and vitamin C tablets.The enzyme-like catalytic reaction based on carbon-based nanozymes provides new insights and approaches for the construction of portable sensors.（2）In this chapter,heteroatom doping and high-temperature pyrolysis were adopted to prepare homogeneous shaped phosphorus-atom-doped carbon-based nanozymes（Fe N₃P）.Compared with the single Fe-N/C material,the catalytic performance of the Fe N₃P was significantly improved,with an approximately 12-fold increase in specific activity.Therefore,in the present experiment,based on the excellent catalytic performance of the Fe N₃P and the inhibitory effect of the enzymatic products of acetylcholinesterase（ACh E）on the catalytic activity,an efficient enzymatic cascade catalytic reaction system was constructed to achieve the colorimetric detection of ACh E activity and methyl parathion content.Under optimal reaction conditions,the sensing system was able to detect ACh E activity and its inhibitor methyl parathion in the ranges of 0.1-10 m U/m L and 0.5-100 ng/m L,respectively,with detection limits of 0.03 m U/m L and 0.13 ng/m L,respectively.It also demonstrates outstanding performance in the analysis of practical samples.In addition,the tandem association of the nanozyme with the natural enzyme achieved catalytic amplification of the enzyme cascade,reducing the ineffective diffusion of intermediates and obtaining a highly sensitive sensor.This work provides a new strategy for the synthesis of high-performance carbon-based nanozymes and the construction of efficient enzyme cascade amplification systems.（3）Iron-doped carbon-based nanoparticles（Fe-NC）with a porous structure were prepared by the templating and hydrothermal methods,and the nanocomposites（Au NPs/Fe-NC）were further synthesized by in situ reduction of chloroauric acid on Fe-NC with trisodium citrate to form gold nanoparticles（Au NPs）.The nanocomposites were capable of catalyzing the production of a variety of reactive oxygen species with the participation of reactive oxygen species and exhibited superior catalytic properties.The kinetic data showed that the prepared Au NPs/Fe-NC exhibited high catalytic activity and substrate affinity,which was attributed to the etching of the template increasing the porous structure and specific surface area of the material,while the loading of noble metal gold nanoparticles with unique physicochemical properties not only increased the active site density of the nanocomposites,but also enhanced the enzyme-like catalytic activity in a synergistic manner.In addition,the quantitative detection of Cr（VI）was achieved by monitoring the change of signal in the system using Au NPs/Fe-NC as the catalyst for the colorimetric sensor,TMB as the chromogenic probe,H₂O₂ as the electron acceptor and 8-hydroxyquinoline（8-HQ）as the inhibitor.The sensor has a linear range of 0-625?M and a detection limit of 0.25?M.It has been successfully applied to the detection of Cr（VI）in water samples with recoveries between 96.2%and 104.21%,and also has promising applications in the fields of colorimetric sensing,analytical detection and environmental protection.