Effect Of Oxygen Content On Properties Of Fluorescent Carbon Nanodots

Carbon nanodots（CNDs）mainly consist of graphene quantum dots（GQDs）and carbon dots（CDs）.Compared with traditional quantum dot materials,CNDs has the advantages of small size,good biocompatibility and low toxicity,which makes CNDs widely used in the field of biosensor and bioimaging.In this paper,based on the special structural site of CNDs,CNDs was used as bipyridine Ruthenium(Ru（bpy）₃²⁺)electrochemiluminescent（ECL）co-reaction reagent and nano-enzyme activity,and the effect of oxygen content on the co-reaction reagent efficiency of CNDs and nano-enzyme activity was investigated respectively.And build based on the electrically induced chemical luminescence of CNDs,ECL biosensor and nano-enzyme catalytic sensor.This thesis is divided into four chapters.Chapter 1:Introduction.The classification,fluorescence characteristics,preparation methods,modification techniques and applications of CNDs in sensing technology are reviewed.Finally,the main research content of this paper is introduced.Chapter 2:The CDs were prepared in the aqueous solution by electrooxidation.The CDs was oxidized by H₂O₂ to obtain CDs@H₂O₂.The size,fluorescent spectrum,and structures of both CDs and CDs@H₂O₂ were characterized by transmission electron microscopy（TEM）,fluorescence spectrophotometer,Fourier transform infrared spectroscopy（FT-IR）,and X-ray photoelectron spectroscopy（XPS）.The results show that there are more hydroxyl groups on the surface of CDs@H₂O₂ than that of CDs.When CDs and CDs@H₂O₂ were respectively used as coreactant of anodic ECL of Ru（bpy）₃²⁺,the ECL signal of is 8.2 times higher for Ru（bpy）₃²⁺/CDs@H₂O₂ system compared to Ru（bpy）₃²⁺/CDs system.Based on the quenching effect of dopamine（DA）on the ECL signal of Ru（bpy）₃²⁺/CDs@H₂O₂ system,an ECL quenching sensor for DA was constructed.The detection linear range was 1.6～56μmol/L and the detection limit was 0.23μmol/L（S/N=3）.The concentration of DA in human serum was detected successfully.This paper provides a method for improving the activity of CDs as Ru（bpy）₃²⁺coreactive agent,and can realize the quantitative detection of DA.Chapter 3:Apart from the noticeable photoluminescent properties,GQDs have exhibited as powerful coreactants for the anodic ECL of Ru（bpy）₃²⁺in recent studies.A universal approach to integrate the Ru（bpy）₃²⁺and coreantants（oxygen-rich GQDs）in a single molecule was developed to enhance the luminous efficiency.Due to the more efficient electron transfer in the intramolecular,the covalently-linked Ru（bpy）₃²⁺-GQDs（Ru-GQDs）hybrid exhibited more efficient ECL than the uncoupled Ru（bpy）₃²⁺/GQDs system.This self-enhanced ECL approach shows great potential in the trace analysis.Based on the quenching effect of pentachlorophenol（PCP）on the ECL signal of Ru-GQDs system,the ECL quenching sensor of PCP was constructed.The detection linear range was 2.00×10^-12～4.70×10^-11 mol/L,and the detection limit was 2.36×10^-13mol/L（S/N=3）.And can realize the trace analysis of PCP in the environment.Chapter 4:GQDs with low oxygenous content and oxidized GQDs（GOQDs）with high oxygenous content were prepared by the ultrasonic stripping and the oxidation of graphite nanoparticles,respectively.The size,structure,fluorescent property,and electron transfer rate of both GQDs and GOQDs were characterized by TEM,FT-IR,fluorescence spectrophotometer,and electrochemical impedance spectroscopy（EIS）,respectively.Both GQDs and GOQDs exhibited the peroxidase-like activity,and could catalytically oxidize the colorless 3,3’,5,5’-tetramethylbenzidine（TMB）by hydrogen peroxide（H₂O₂）into a blue solution.The catalytic reaction was followed the Michaelis-Menten kinetic model and the Michaelis constants（k_m）for H₂O₂ by GQDs and GOQDs as peroxidase was 26.19 mmol/L and 15.88 mmol/L,respectively.The results show that GOQDs with high oxygenous content had high catalytic activity as peroxidases.The linear range of GOQDs for H₂O₂ detection was 0.002～2.4 mmol/L with the detection limit（S/N=3）was 0.4μmol/L,which provides a simple and effective method for H₂O₂detection.