Green Synthesis,Photoluminescence Mechanism Of Functional Cellular Carbon Dots And Their Applications In Cell Targeted Imaging Analysis

Carbon is one of the most abundant natural elements,in recent years,carbon-based nanomaterials have attracted wide interest in different fields.Carbon dots(CDs),as a new type of photoluminescent(PL)carbon nanomaterials,have been widely applied to biochemical analysis,cellular imaging,drug delivery,catalysis and optical devices owing to their excellent optical properties,good water solubility,photostability and low toxicity.However,the traditional methods reported of synthesis CDs have the disadvantages of low quantum yield and the need to provide large heat sources during the synthesis process.In recent years,methods for preparing carbon dots at room temperature have been established using strong acids,alkalis,and strong oxidants,which require tedious work and could have much dangerous.In this thesis,we prepare a series of carbon dots by select the precursor,and discuss the formation and photoluminescence mechanism,ultimately apply them in biochemical analysis and lysosome targeting imaging.The detail research contents consist of the following three parts:(1)Solvethermal synthesis of carbon dots for detection of hematin based on inner filter effect(IFE).In this work,the blue emission CDs were prepared through a facile solvethermal method by reasonably choosing p-aminobenzoic acid(PABA)and ethanol as raw materials.The as-prepared CDs had excellent stability and hydrophily,making it possible to act as a perfect fluorescent probe.High resolution transmission microscope(HRTEM),Atomic force microscopy(AFM)and Raman spectroscopy showed that the CDs were multi graphene layers quasi spherical nanoparticles,with both sp~2 and sp~3 C.Fourier transform infrared spectroscopy(FTIR)and X-ray photoelectron spectroscopy(XPS)results showed that there were abundant amino and carboxyl groups on the surface of the CDs.More importantly,there was a good spectral overlap between the excitation and emission spectra of the CDs and the absorption spectra of hematin which has a large molar absorption coefficient,resulting in a selective detection method of hematin based on IFE.What's more,the method has been successfully applied for hematin determination in healthy human red cells,showing CDs has a great potential prospect for detection of hematin in the complex matrixes.(2)Synthesis of emerald carbon dots(ECDs)at room temperature for lysosome targeting and lysosomal pH imaging.It is reported that amino groups and abundant hydrophilicity groups could achieve cell lysosome targeting.So,we reasonably selected p-benzoquinone and ethanediamine as raw materials for preparing high quantum yield ECDs at room temperature,taking a functional group protection strategy(FPS).Through a series of characterization of ECDs,it was proved that ECDs had abundant amino and hydrophilic groups(carboxyl,hydroxyl),which leaded to the sensing of pH by the protonation and deprotonation of hydrophilic groups on the surface of ECDs in vitro.And the Boltzmann equation showed the p Ka of ECDs was 4.78,which perfectly covered the lysosome pH(4.5-5.5),while the abundant amino and hydrophilic groups of ECDs induced its target lysosome actively.The co-localization results of ECDs with commercial lysosomal dye(Lyso-Tracker Red)showed that the ECDs could target lysosome ideally.Finally,the ECDs were using for monitor the lysosomal pH dynamics during apoptosis in live cells.(3)Rationally designed carbon dots at low temperature with a surface-state-controlled photoluminescence mechanism.Based on the second work,choosing the same raw materials p-benzoquinone and ethanediamine,we prepared a series of high quantum yield CDs-1,CDs-2,CDs-3,CDs-4 and CDs-5 at different reaction temperatures(35?,25?,15?,0?,-15?).As the theoretical calculation results showed,even at low ambient temperature,p-benzoquinone and ethanediamine could also react spontaneously and undergo the process of dehydration,carbonization and polymerization finally formation of carbon dots.By carfully researching the characterizations of CDs,it was showed that all CDs had different particle size,carbon core state with similar elemental composition and functional groups,however,percentage of functional groups was different.Moreover,the maximum excitation wavelength and emission wavelength of CDs were all at 400 nm and 530 nm,but the quantum yield increased with reaction temperature increasing,which should be explained by the surface oxidation of different CDs.And the fluorescence lifetimes of the five carbon dots are similar,the excited state energy level(lowest unoccupied orbital,LOMO)and the ground state energy level(highest occupied orbital,HOMO)were slightly different,further confirming that their photo luminescence properties are similar.All results showed that the photoluminescence mechanism of the CDs was not related to the carbon core,but mainly depends on the surface oxidation state of the CDs.In summary,we selected the raw materials rationally of all three works.The preparation methods of CDs were improved from the traditional solvethermal method to room temperature method,which expanded the synthesis methods of carbon dots.The selective detection of hematin in human red cells was achieved in vitro.And we successfully applied ECDs for lysosome targeting and lysosomal pH imaging which expanded the application of carbon dots.Finally,we synthesized different CDs by controlling the reaction temperature and explained the photoluminescence mechanism of CDs with a surface-state-controlled mechanism,which largely enriched the theory research of CDs.We hope our whole work can provide valuable information for green preparation,organelle targeting and photoluminescence mechanism of carbon dots,and broadening the application of CDs in future research.