Studies On The Synthesis Of Heteroatom-Doped Carbon Dots And Their Application In Pharmaceutical Analysis And Cellular Imaging

Carbon dots?CDs?have spurred tremendous interests in recent years due to their superior optical,electronic and biocompatible properties,which enable their applications in the fields such as biosensing,bioimaging,drug delivery,photocatalysis,and energy conversion etc.However,to date,most of reported CDs show low quantum yields,short emission wavelengths,difficulty in modification,making CDs impossible to replace traditional semiconductor quantum dots or organic fluorescent molecules.Also,studies in the origin of optical and electronic properties of CDs,and their controlled synthesis are limited,still in their infant stage.Hence,it is highly desirable to explore their optical and electronic properties,optimal synthetic methods to obtain CDs with high photoluminescence and long emission wavelengths.It is also attractive to extend applications of CDs in more urgent and pressing field such as pharmaceutical analysis and real-time imaging.In this thesis,we prepare a series of carbon dots and investigate their optical properties and biocompatibility in detail;ultimately apply them in drug analysis and cellular imaging.The detail research contents consist of the following three parts:1.Microwave synthesis of sulphur and nitrogen-doped highly photoluminescent carbon dots for tetracycline hydrochloride?Tc?sensing based on inner filter effect?IFE?.In this work,the fluorescent carbon dots?CDs?were prepared through a facile microwave route by using citric acid?CA?as carbon source,glutathione?GSH?as N,S source in the fashion of doping in order to improve the quantum yields?QY?of the product.The QY of CDs is high up to 46.9%.The synthetic process,optical,bio-chemical properties of CDs were discussed in detail through characterization of structure,morphology,functional groups of the product.It was found that the obtained CDs had advantages of excitation-independent PL emissions behavior,low toxicity,excellent optochemical stability,making it possible to act as a perfect fluorescent probe.More importantly,there is a good spectral overlap between the absorption band of the Tc and the excitation or emission of the CDs,and Tc has a relatively large molar absorption coefficient,suggesting that the detection method of Tc could be established based on IFE.For evaluation the sensitivity of Tc detection,the value of F₀/F was in the linear relationship along with concentrations of Tc from 2 mM to 150 mM,with a limit detection of 0.52 mM.Subsequently,the CDs were loaded into electrospun nanofibers to develop a visual sensor for Tc recognition in solid state,showing excellent selectivity.Compared to some common systems such as fluorescence resonance energy transfer?FRET?,photoinduced electron transfer?PET?,IFE-based method is more simple,flexible and cost-efficient.In brief,this IFE-based exploration will pave a new way for the determination of Tc in the real world.2.Nitrogen and phosphorus doped polymer carbon dots?PCDs?as a sensitive cellular imaging probe of nitrite.PCDs doped with nitrogen and phosphorus were prepared by acid reacting a mixing solution of ascorbic acid?AA?and polyethylenimine?PEI?at low temperature through a route involving acid catalysis,dehydration,polymerization and carbonization.The obtained PCDs exhibited excellent stability,adjustable fluorescence emissions and good biocompatibility,making it possible to be applied for biosensing and real-time cellular imaging.The elements,functional groups and surface charge of PCDs were analyzed through XPS,FTIR,Zeta-potential characteristics,demonstrated that PCDs were formed with AA as core and PEI polymer as shell.Therefore,the redox reaction between PEI and nitrite?NO₂?may result in fluorescence quenching of PCDs,similar to reported literature.PCDs showed excellent selective response towards NO₂,as other metal ions and anions such as Al3+,Ca2+,Cr3+,K+,Ac-,Br-,Cl O-3 had no obvious quenching effect on PCDs.More importantly,the as-prepared PCDs could be employed for dynamic monitoring of NO₂ entry into HEp-2 cells.This noticeable phenomenon suggests PCDs may have a great potential as a high-performance luminescent platform for tracking NO₂ in living cells.In addition,we also investigate the intracellular behaviors of PCDs,implying that the cellular uptake PCDs is via lysosome pathway.The distribution of PCDs is dynamic from cell membrane to asymmetric perinuclear region known as microtubule organizing center?MTOC?.All the results show the obtained PCDs are promising to broaden applications in the fields of analysis and bioimaging.3.One-pot synthesis of yellow fluorescent carbon dots for detection of copper ions(Cu²⁺)and glutathione?GSH?based on aggregation induced enhanced emission?AIEE?.In this work,we used o-diaminobenzene?OPD?as carbon source to hydrothermally synthesize carbon dots with yellow emission wavelength.The XPS and FITR results show CDs have rich amino group,making it possible to bind with Cu²⁺.We carried out a series of experiments to demonstrate that the CDs-Cu²⁺ complex could form into large aggregates.The fluorescence intensities of OPD-CDs increased dramatically due to AIEE phenomenon.This method exhibited high sensitivity and selectivity towards Cu²⁺ assay.Moreover,after adding GSH into the OPD-CDs-Cu²⁺ system,the FL intensities of CDs decreased to their original level.This phenomenon may possibly due to the stronger bonding between GSH and Cu²⁺,resulting in disassembly of OPD-CDs-Cu²⁺ complex.Our AIEE-based method can be applied for simultaneous detection of Cu²⁺ and GSH.In summary,we explored facile methods to prepare CDs with high quantum yield,long emission wavelengths and good biocompatibility via selecting proper precursors.Meanwhile,we also studied the synthetic process,optical properties of CDs and got deep understanding of their luminescence mechanism.Ultimately,we employed CDs as fluorescent probes to establish a series of assay methods for sensing pharmaceutical molecules such as Tc,GSH,etc.The obtained CDs could also be used as imaging agent and their intercellular behaviors were also investigated.We hope our whole work can provide valuable information for preparing CDs with high QY,and broadening the application of CDs in future research.