Application Of Doped Metal Carbon Quantum Dots In The Analysis Of Environmental Biological Samples

Carbon quantum dots（CDs）,as a new spherical fluorescent nano luminescent material with diameter less than 10 nm,have many advantages over other quantum dots,such as excellent optical properties,easy functionalization and preparation,good water solubility,low toxicity,easy surface modification and so on.They have been widely used in many fields and become a hot spot in the research of nano materials in recent years.However,due to the complexity of environmental biological samples,there are more and more requirements for the sensitivity,specificity and accuracy of CDs.There are many challenges in the analytical application,such as low quantum yield,lack of surface groups,and many interference factors on the fluorescence intensity,which lead to low recognition ability,low accuracy,and certain limitations of specific binding ability.At present,many scholars use doping to improve the optical and electronic properties of CDs.In particular,compared with many nonmetal heteroatom doping,metal ion doping has larger atomic radius and better electron mobility,which greatly changes the physical and chemical properties of CDs.Based on this,in this paper,three kinds of CDs with different properties were prepared by hydrothermal method by doping metal ions,and three sensors for environmental biological sample analysis were constructed,and the biological imaging research was carried out.The main research contents are as follows:1.Mg doped carbon quantum dots（Mg-CDs）with unique optical properties were synthesized by one pot hydrothermal method and characterized by transmission electron microscopy（TEM）and atomic force microscopy（AFM）.The optical properties of Mg-CDs were studied by fluorescence and ultraviolet spectroscopy.Since Mg doping exists in the form of Mg²⁺,the metal ions first bind to the phosphate group of ATP,resulting in ATP quenching the fluorescence of Mg-CDs.In the presence of arginine,arginine and Mg²⁺can hydrolyze ATP,and the electrostatic interaction between arginine and phosphoric acid has covalent stability,which makes arginine and ATP form competitive binding,leading to the breaking of phosphate group of Mg²⁺and ATP,and the fluorescence recovery of Mg-CDs.Therefore,the detection of arginine in human urine by Mg-CDs is realized.Under the optimized conditions,the linear range of arginine was 0.3-130μM,and the detection limit was 0.15μM.The recoveries were 97%-100.4%.2.Using citric acid,ethylenediamine and zirconium chloride as raw materials,zirconium and nitrogen Co doped carbon quantum dots（Zr-N-CDs）were synthesized by hydrothermal method.The quantum yield of doped carbon quantum dots was up to 82.7%,which had very good water solubility in aqueous solution.The Zr-N-CDs were characterized by transmission electron microscopy（TEM）and atomic force microscopy（AFM）.The optical properties of Zr-N-CDs were studied by fluorescence and UV spectra.Because the absorption peak of Cr（VI）overlaps with the excitation peak and emission peak of Zr-N-CDs,the fluorescence resonance energy transfer（FRET）is induced and the fluorescence of Zr-N-CDs is quenched.Under the optimized experimental conditions,there was a good linear relationship between Cr（VI）concentration and fluorescence quenching efficiency of Zr-N-CDs in the range of0.4-100μM,and the detection limit was 0.52μM.In addition,by using the prepared Zr-N-CDs,we analyzed the speciation of chromium in natural waters.That is to say,hydrogen peroxide（H₂O₂）is used to convert Cr（III）into Cr（VI）,and the total content of Cr is determined.Therefore,the content of Cr（III）is determined by subtracting the content of Cr（VI）from the total content of chromium.The recoveries of spiked samples in natural waters ranged from 98.35%to 100.9%.The reproducibility was 1.52%-2.89%（RSD%,n=3）.The results show that the quantum dots have good accuracy and no obvious matrix interference,which have a very good application prospect in water sample detection.The cytotoxicity of Zr-N-CDs to He La cells showed that Zr-N-CDs had no obvious cytotoxicity.Therefore,the application of Zr-N-CDs in cell biological imaging was confirmed by laser confocal microscopy.3.Cerium nitrogen Co doped carbon quantum dots（Ce-N-CDs）were synthesized by hydrothermal method using citric acid,ethylenediamine and cerium nitrate as materials.The doped carbon quantum dots have good water solubility and high quantum yield（QY=93.14%）.The Ce-N-CDs were characterized by transmission electron microscopy（TEM）and atomic force microscopy（AFM）.The optical properties of Ce-N-CDs were studied by fluorescence and UV spectra.Ce-N-CDs was used to detect tetracycline（TCs）drug residues based on internal filtration effect（IFE）.The carbon quantum dots showed high selectivity for tetracycline（TCs）drugs.Taking doxycycline（DC）,a member of tetracycline family,as the representative,under the premise of optimizing the experimental conditions,the results show that the fluorescence quenching efficiency of Ce-N-CDs has a good linear relationship with the concentration of doxycycline（DC）in the range of 0.4-35μM,and the detection limit is0.25μM.The recoveries were 92%-107.06%.The reproducibility was 1.05%-2.84%（RSD%,n=3）.The results show that Ce-N-CDs has very good accuracy and no obvious interference matrix,so it has a good application prospect in food monitoring.In addition,the Ce-N-CDs synthesized by hydrothermal method had low cytotoxicity and did not effect on cell viability.The application of Ce-N-CDs in Hep G2 cell imaging was studied.