Preparation,ROS Activities And Peroxide-Like Properties Study Of Heteroatomic Doped Carbon Dots

Carbon dots（CDs）are new class of light-emitting carbon based nanomaterials,and have the advantages of good biocompatibility,low toxicity,high water solubility and excellent optical properties.CDs play important role in biosensing,drug delivery,cell imaging,photothermal therapy and mimic enzyme.However,CDs prepared from a single carbon source have disadvantages such as fewer active sites,low electron density and weak electron transfer abilities,those induce the nonobvious activities of Reactive Oxygen Species（ROS）and Peroxidase（POD）.It has been reported that heteroatomic doping can increase the electron density of CDs,provide more catalytic and substrate binding sites,and thus improve the ROS activity and POD performance of CDs.Therefore,heteroatom doping becomes an optimal strategy to promote the development of CDs.Abnormal ROS levels in human body will cause many diseases.Therefore,effective regulation of ROS activity is of great significance.POD is the earliest artificial simulated enzyme among natural enzymes,but there are many research spaces in improving enzyme activity and exploring the catalytic mechanism of simulated enzymes.In this experiment,nitrogen doped carbon dots（N-CDs）,nitrogen sulfur doped carbon dots（N,S-CDs）and nitrogen iron doped carbon dots（N,Fe-CDs）were prepared by hydrothermal method and characterized by transmission electron microscopy（TEM）,Fourier transform infrared spectroscopy（FT-IR）,X-ray photoelectron spectroscopy（XPS）,X-ray diffraction（XRD）,Ultraviolet-visible absorption spectrum（UV-Vis）and fluorescence spectra（FL）.etc.ROS activity of N-CDs,peroxidase properties of N,S-CDs and N,Fe-CDs were also investigated.The main research results were summarized as follows:（1）N-CDs were synthesized from citric acid and dicyandiamine by hydrothermal method.The morphology and structure of N-CDs were characterized by TEM,XRD,FT-IR and XPS.The results showed that N-CDs have spheroid structure with an average particle size of 5.5nm and exist in the form of amorphous carbon.N-CDs can remove·OH free radicals produced from Fenton reaction.¹O₂ can be produced under NIR（650 nm）irradiation,both of which can inhibit the formation of Aβ₄₂ aggregates.Therefore,N-CDs can be used for the depolymerization of Aβ₄₂ aggregates.（2）N,S-CDs were synthesized by hydrothermal method from citric acid,L-lysine and thiourea.The morphology and structure of N,S-CDs were characterized by TEM,XRD,FT-IR and XPS.The results showed that N,S-CDs have spheroid structure with an average particle size of 6.0 nm and exist in the form of amorphous carbon.N,S-CDs have peroxisme-like activity,and the steady-state kinetic experiment results showed that follow the typical Michaelis-Menten equation,N,S-CDs have strong affinity for both TMB（K_m=0.228）and H₂O₂（K_m=0.7536）.Through EPR,Rh B probe and electrochemical experiments,the catalytic mechanism of N,S-CDs peroxidase was investigated,and it was found to be consistent with the electron transfer process.（3）N,Fe-CDs were synthesized by hydrothermal method from Ammonium iron（Ⅲ）citrate and dicyandiamine.The morphology and structure of N,Fe-CDs were characterized by TEM,XRD,FT-IR and XPS.The results showed that N,Fe-CDs have spheroid structure with an average particle size of 4.5 nm and exist in the form of amorphous carbon.N,Fe-CDs showed high peroxidase activity,and in the presence of H₂O₂,it could catalyze the typical oxidation reaction of substrate TMB,with strong affinity for TMB（K_m=0.423）and high catalytic reaction rate(V_max=12.15×10^-8 M·s^-1).Through EPR and Rh B probe experiments,it was concluded that the peroxidase catalytic mechanism of N,Fe-CDs was due to the formation of·OH radical.In addition,based on Peroxide-like activity of N,Fe-CDs,H₂O₂ and AA were detected by colorimetry.The detection range of H₂O₂ was 1-100μM,and the detection limit was 0.40μM.The detection range of AA was 1-50μM,and the detection limit was 2.05μM.