Synthesis Of Carbon Dot Based Nanomaterials And Their Application In Photodynamic Therapy Of Tumors

Malignant tumor is one of the major factors leading to the death of the world's population.It not only endangers human life and health,but also greatly restricts the development of the national economy.Therefore,timely diagnosis and treatment of malignant tumor has become an urgent matter of the moment.Photodynamic therapy(PDT),as one of the many methods to treat malignant tumors,has greatly reduced the damage caused by traditional treatment methods such as radiation,chemotherapy and surgery.PDT is to inject photosensitizer into the tumor site,and then irradiate the tumor site with the corresponding wavelength of light to activate the photosensitizer,and produce a large amount of reactive oxygen species(ROS),thus triggering the apoptosis of tumor cells,resulting in the rupture of tumor,and achieving the therapeutic effect.Therefore,photosensitizers play an important role in the process of tumor PDT.However,although a series of photodynamic photosensitizers represented by hemoporphyrin have a high ROS production rate,they are restricted by poor water solubility and low biocompatibility,which greatly reduce the effect of photodynamic therapy and limit their long-term development in the field of photodynamic therapy to some extent.Therefore,the use of carbon dot based nanomaterials with high ROS production rate,excellent water solubility and good biocompatibility as a new type of photosensitizer has attracted much attention.In recent years,as a member of the family of carbon nanomaterials,carbon dot(CD) has attracted the attention of many researchers.Besides the basic properties such as low raw material cost,low toxicity and good biocompatibility,it also has a series of unique properties,including fluorescence tunability,photobleaching resistance and certain phototoxicity for cancer cells,which can be used in biomedical fields such as photodynamic therapy(PDT),photothermal therapy(PTT)and photoacoustic imaging(PA).The emergence of CDs not only greatly reduces the use cost of nanomaterials,but also broadens the application field of carbon-based nanomaterials.However,under normal circumstances,the structure stability and crystallinity of common CDs are poor,and it is easy to be affected by external conditions and leading to fluorescence quenching.The physical and chemical properties of some CDs doped with heteroatoms will be thoroughly altered.In this study,Sn nanocluster-wrapped CDs(Sn nanocluster@CDs)and halogen Chlorine doped GQDs(Cl-GQDs)with PDT potential were synthesized.Their structures,morphology and properties were characterized,and their applications in cell development,in vivo and in vitro PDT were studied.The main research contents and results are as follows:First,using sodium styrene sulfonate as raw material,S-CDs was prepared by one-step thermal decomposition method,and then a certain concentration of Sn Cl₄ solution was added into S-CDs solution to obtain the precursor Sn⁴⁺@S-CDs after ultrasound.Then the solid precursor was fully dissolved in deionized water,and then freeze-dried into powder to obtain Sn nanocluster@CDs.The synthesized Sn nanocluster@CDs was characterized by transmission electron microscopy(TEM)and particle size distribution.The obtained Sn nad particle size was 2.27 nm,and the absolute fluorescence quantum yield(QY)increased from 2.70 to 4.60.In addition,normal mouse tissue cells(CHO)and breast cancer cells(4T1)were selected as cell models,and tetramethylazolium salt assay(MTT)was used to test the cytotoxicity of synthesized Sn nanocluster@CDs.It was found that when the concentration of Sn nanocluster@CDs co-culture with CHO and 4T1 cells increased to 300?g m L^-1,the survival rate of the two cells was still higher than 80%,indicating that the cells had low cytotoxicity.In addition,after the Hep G2cells were co-cultured with Sn nanocluster@CDs for 4 h,the Sn atoms were observed to fluoresce brightly in the cytoplasm under confocal laser microscopy,indicating that Sn atoms have potential application value in biological imaging.In order to estimate the photodynamic therapy(PDT)effect of Sn nanocluster@CDs,electron paramagnetic resonance spectroscopy(ESR)analysis was taken out,showing that under the irradiation of LED light(400-700nm,40m Wcm^-2),the Sn nanocluster@CDs could produce singlet oxygen(¹O₂).In addition,rose-bengal(RB)was selected as ¹O₂ quantum yield reference agent and 9,10-anthracylbis(methylene)dialoic acid(ABDA)was selected as the capturing agent.The decomposition rate of¹O₂ generated by Sn nanocluster@CDs to ABDA was tested by ultraviolet absorption method.The calculated ¹O₂ quantum yield of Sn nanocluster@CDs was 58.3%.Hep G2cells were used as cell model,and the PDT effect of photoinduced Sn nanocluster@CDs was detected by MTT assay and living/dead cell staining method.It was found that light and Sn nanocluster@CDs concentration were important factors affecting PDT.In addition,SPF Balb/C mice loaded with 4T1 tumor were used as the model to test the effect of PDT of Sn nanocluster@CDs in vivo.The results indicate that Sn nanocluster@CDs may have a great application prospect in the field of fluorescence imaging and PDT treatment.Secondly,the precursor graphene(GO)was prepared from flake graphite through the improved Hummers method,then the GO was cut into oxidized GQDs by hydrogen peroxide oxidation cutting method.Then the GO was mixed with and NH₄Cl in a certain proportion,and oxidized by hydrogen peroxide cutting method.Finally,Cl-containing heteroatom doped graphene quantum dots(Cl-GQDs)were purified.Then,the morphology,structure and fluorescence properties of the obtained GQDs and Cl-GQDs were characterized.The results showed that both GQDs and Cl-GQDs had good water solubility.GQDs showed a typical wavelength dependence of unexcited light,while Cl-GQDs showed a certain dependence of excited light with the addition of halogen heteroatom.In addition,they all exhibit good photostability.To further explore the property of the material,the ESR has also been carried out,showing that the singlet oxygen signal of Cl-GQDs is stronger than that of GQDs.The results showed that Cl-GQDs may have higher ¹O₂ production rate compared with GQDs,with better PDT effect.Finally,using He La cells as the model of PDT experiment in vivo and mouse breast cancer cells 4T1 as the model of PDT in vivo experiment,showing that Cl-GQDs had the potential to be a photosensitizer for tumor PDT.