Application Of Functionalized Carbon Dots In Ion Detection And Cell Antioxidation

Carbon dots（CDs）are nanomaterials composed of sp²/sp³ hybridized carbon nuclei,whose size is usually less than 10 nm.They have shown a wide range of applications in ion detection,bioimaging,drug delivery,and medical therapy due to their abundant functional groups on the surface and unique optical properties.The work in this thesis is focus on the synthesis of carbon dots,the functionalized modification of carbon dots,and the application of carbon dots in ion detection and cellular antioxidant as follows:（1）Preparation and characterization of two carbon dots:In this paper,two types of carbon dots were synthesized.Firstly,a mixed solution of carbon dots was obtained by hydrothermal method using citric acid as the raw material and formamide as the organic solvent,and then purified by centrifugation and dialysis to obtain an aqueous solution of CDs.Manganese sulfate solution was then added to it to obtain carbon dots doped with manganese elements.Through a series of characterizations such as TEM and XPS,it was determined that the particle size of the carbon dots before and after doping was in the range of 2-5 nm,which was approximately spherical;the manganese element was successfully attached to the CDs through the carbonyl group on the surface of the CDs,and the addition of manganese element did not change the crystalline structure of the original CDs;the carbon dots before and after doping had good fluorescence stability（such as salt tolerance,anti-photobleaching,optical stability,etc.）,multi-color emission and other optical properties.（2）Specific detection of Fe³⁺by CDs:The detection of common ions by CDs showed that Fe³⁺burst CDs were the most effective,indicating that the CDs could be used for the detection of Fe³⁺in the range of 25μM-350μM,and the CDs showed good linearity for the detection of iron ions with a detection limit of 6.4μM.The average fluorescence lifetime analysis of quenching of CDs by Fe³⁺showed that the burst mechanism was static burst,indicating that the CDs had a good affinity for Fe³⁺and could interact strongly with the abundant functional groups on the surface of CDs.Furthermore,the assay was successfully applied to the detection of Fe³⁺in tap water and macrophages（RAW264.7 cells）.（3）Protective functions of Mn-doped CDs（Mn-CDs）against oxidatively damaged cells:Mn-CDs possess good SOD-like enzyme activity and ABTS and DPPH radical scavenging abilities.The protective effects of Mn-CDs on oxidatively damaged cells were investigated by establishing an in vitro oxidative stress model.In the oxidative stress cell model,Mn-CDs could significantly reduce intracellular ROS content,increase the membrane potential of mitochondria,improve intracellular Ca²⁺homeostasis,reduce apoptosis,and play a better protective role compared to cells in the control group.In summary,carbon dots were successfully prepared and Mn-doped modification studies were performed in this paper.The results show that CDs and Mn-CDs not only have good fluorescence stabilization properties,but also can achieve colorful fluorescence imaging in cells.Furthermore,CDs can specifically bind to Fe³⁺to detect Fe³⁺in tap water and cells;Mn-CDs are biocompatible and can scavenge ROS in RAW264.7 cells,thus reducing the oxidative damage of cells and playing a protective role.