Metal-doped Carbon Dots As Peroxidase Mimics For Quantitative Detection Of Hydrogen Peroxide And Glucos

Carbon dots（CDs）is a new type of zero dimensional quasi spherical carbon nano material that has attracted much attention in recent years.Carbon dots has several superior characteristics including sufficient carbon sources,easy preparation,no toxicity,and high catalytic efficiency as a new kind of nanozyme.Doping with different elements,especially metal-doped carbon dots have been carried out to improve the enzymemimicking activities of CDs.Based on the variable valence state of the metal and enhanced electron transfer（both electron donating and accepting）abilities,several kinds of single and multiple metal were doped into carbon dots,which show better peroxidemimetic enzyme activity.Here,we choose Ce,Cr,Cu,Fe,Mn as the doped metal element,which tend to increase the surface electron charge of CDs structure to form active sites.Ce doped carbon dots（Ce-CDs）,Cr doped carbon dots（Cr-CDs）,Cu doped carbon dots（Cu-CDs）,Fe doped carbon dots（Fe-CDs）,Mn doped carbon dots（Mn-CDs）and metal free doped carbon dots（0-CDs）have been synthesized via simple hydrothermal method by using citric acid as carbon source.The synthesized CDs as peroxidase mimics to offer a high sensitivity and selectivity colorimetric method for H2O2 and glucose determination in real samples.Meanwhile,based on fluorescence quenching,a fluorometric method for H₂O₂ detection was also built.This system provides a simple,sensitive and selective method for the determination of hydrogen peroxide and glucose.The main research work is as follows:（1）Quantitative detection of hydrogen peroxide using carbon dots as fluorescent probesCarbon dots were successfully prepared by one-pot hydrothermal method with citric acid as carbon source and metal nitrate as metal source.The synthesized carbon dots were characterized by high resolution transmission electron microscope,Fourier transform infrared spectrometer,X-ray photoelectron spectrometer,X-ray diffractometer,UV absorption spectrum and fluorescence spectrophotometer.The results show that the carbon dots doped with metal elements have been successfully synthesized with small particle size,excellent water-solubility,adjustable emission and fluorescence stability.Fluorescence quenching is occurred when hydrogen peroxide is added,a good linear relationship between the fluorescence intensity of carbon dots and the concentration of hydrogen peroxide can be obtained.It is reported that the emission of carbon dots is due to the defects on the surface of carbon dots.In the whole reaction process,hydrogen peroxide,as an oxidant,will release hydroxyl radicals when catalyzed by carbon dots with peroxide mimic enzyme properties,resulting in changes in the surface of carbon dots,especially the surface energy trap of carbon dots will be destroyed,thus the fluorescence intensity of carbon dots will be reduced.A fluorescence detection method for the quantitative detection of hydrogen peroxide by carbon dots is successfully constructed and applied to the detection of hydrogen peroxide in infant milk powder.The detection results are accurate and reliable,which prove that this method can be applied to the detection of actual samples.Fe-CDs shows the highest sensitivity toward H2O2 detection.（2）Metal doped carbon dots were used as peroxidase mimetic enzyme to quantitatively detect hydrogen peroxide and glucoseMetal element doped carbon dots were prepared by the same synthesis method as above.Herein,Ce doped carbon dots（Ce-CDs）,Cr doped carbon dots（Cr-CDs）,Cu doped carbon dots（Cu-CDs）,Fe doped carbon dots（Fe-CDs）,Mn doped carbon dots（Mn-CDs）and non-metal doped carbon dots（0-CDs）exhibit peroxidase-like activity.By using metal doped carbon dots as peroxidase simulation enzyme and 3,3 ’,5,5’-tetramethylbenzidine（TMB）as substrate,CDs can catalyze the oxidation of TMB by hydrogen peroxide to form oxidized TMB（ox-TMB）with an absorption peak at 652 nm.Given that glucose can be catalyzed and oxidized by glucose oxidase（GOD）under aerobic conditions to produce gluconic acid and hydrogen peroxide,a convenient colorimetric method for glucose determination is also developed.The results show that Fe-CDs possess the highest catalytic activity,the detection limit of this assay for glucose was 0.029 mmol L^-1,when using Fe-CDs as peroxidase mimetic.This successfully provides a sensitive and selective colorimetric method for hydrogen peroxide and glucose determination.