Functionally Modified Graphite Phase Carbon Nitride Nanosheets And Their Applications

As a new two-dimensional metal-free semiconductor nanomaterial,graphite phase carbon nitride has shown good application prospects in the fields of photocatalysis,electrocatalysis and optoelectronics.Graphite-phase carbon nitride nanosheets show potential for biomedical applications,bioimaging,fluorescence detection,drug delivery,and photodynamic therapy because of their advantages such as good biocompatibility,low toxicity,high fluorescence quantum yield,and an extendedπ-conjugated system.As a new type of non-invasive anti-cancer therapy,sonodynamic therapy has attracted great interest of researchers in the field of tumor therapy.Ultrasound can activate the sensitizer compounds accumulated in tumors,thereby generating high reactive oxygen species,such as singlet oxygen and superoxide radicals,causing irreversible tissue damage to the tumor.And ultrasound has strong tissue penetration ability,so sonodynamic therapy is very suitable for the treatment of tumors in deep tissues.Nitric oxide acts as a diffusible free radical signaling molecule in various physiological and pathological processes,including apoptosis,angiogenesis,immune response,and neurotransmission.Nitric oxide gas treatment can overcome the resistance of sonodynamic therapy under hypoxia and enhance the effect of sonodynamic therapy.In addition,nitric oxide itself can induce tumor cell apoptosis.Fluorescence detection is a safe,simple,fast,and sensitive detection method.It has been widely used in the biomedical field in recent years.However,only a few compounds can produce fluorescence,and most molecules do not.Therefore,the development of materials with fluorescent properties has always been a research hotspot in the scientific research field.In this thesis,we prepared carbon nitride nanosheets with fluorescent properties,and explored their applications and effects as fluorescent detection probes and drug delivery probes in the field of biomedicine.The full text is divided into four chapters.In the first chapter,we introduce the properties and applications of carbon nitride materials,sonodynamic therapy and NO gas therapy,and propose the research ideas.In the second chapter,we first prepared OCN nanosheets through two steps of high temperature polycondensation and chemical stripping,and characterized them.Then we modified 6 armed PEG,Ce6,Gd³⁺and NO donor BNN6 to obtained OCN-PEG-(Ce6-Gd³⁺)/BNN6 nanocomposite which have a magnetic resonance imaging performance and can generate reactive oxygen and NO in response to ultrasound.The covalent modification of Ce6 and the loading of BNN6 in the material were calculated,and its magnetic resonance imaging performance in vitro and in vivo and the effect of sonodynamic/NO synergistic treatment were studied.The prepared g-C₃N₄ nanosheets have a flaky morphology and have uniform particle size.In vitro cell experiments with cancer cells and normal cells show that OCN-PEG-(Ce6-Gd³⁺)materials have lower cytotoxicity and better biocompatibility.In vivo and in vitro sonodynamic experiments and NO release experiments show that it has good ROS production and NO release ability under the action of ultrasound.Due to the doping of the Gd element,the material has the capability of magnetic resonance imaging and can be used as a contrast agent for magnetic resonance imaging.The sensitizer Ce6 in OCN-PEG-(Ce6-Gd³⁺)/BNN6 generates reactive oxygen species（ROS）under the stimulation of ultrasound,At the same time,BNN6 releases NO molecules in response to ultrasound to achieve the purpose of killing cancer cells and the effect of sonodynamic/NO synergy therapy.In the third chapter,we prepared the bulk g-C₃N₄ by high temperature polycondensation method and further successfully prepared the g-C₃N₄ nanosheets by ultrasonic pulverization and peeling.G-C₃N₄ nanosheets with different sizes were prepared by controlling the ultrasonic time,and their fluorescence properties and their effects on fluorescence detection applications were compared.Their structures and feature were characterized by fluorescence spectra,UV-vis spectra,FT-IR spectra,XPS and other methods.A new method for the determination of adenine content was developed based on the principle of fluorescence quenching.The results of a series of experiments show that the concentration of adenine in the range of 0.3-1μM has a good linear relationship with the fluorescence quenching rate of fluorescent g-C₃N₄nanosheets,with high accuracy and a detection limit as low as 0.3μM.This proves that the method is highly sensitive.Through spike recovery,the value of this method in the actual determination of adenine content in red blood cell preservation solution was further proved.In the fourth chapter,we summarize the data and results obtained in this thesis about the preparation,characterization of materials and their applications in the field of biomedicine.Finally,the future research and application prospects are discussed.