Preparation And Multifunctional Application Of Heteroatom Doped Fluorescent Carbon Dots

Carbon dots(CDs)were extensively used in environmental and biosensors,biomedical,LED,information security and anti-counterfeiting,due to their unique structural characteristics,such as photoluminescence,biocompatibility,electrochemical and other characteristics.So far,the reported synthesis methods have some problems,such as complex preparation process,high consumption,time-consuming,low fluorescent quantum yield and the production of toxic substances.Therefore,it is of apparent importance for the development of a speedy,environment-friendly and efficient preparation approach.As the most effective way to adjust the fluorescence properties of CDs,heteroatom doping approaches provide technical support for the development of high-performance fluorescent CDs or the expansion of their applications in some specific fields.In this paper,four kinds of heteroatom doped multifunctional CDs with outstanding performance were designed and fabricated by hydrothermal treatment and acid-base neutralization reaction.The prepared CDs were characterized and used in many fields such as,determination of metal ions,vitamins,quercetin and H₂S,biological imaging,antioxidant,antibacterial,and fluorescent anti-counterfeiting.Chapter 1:The structure,optical properties,preparation methods and luminescent mechanism of CDs were summarized.The regulation of fluorescence properties of CDs and their research progress in the fields of analysis and detection,antibacterial,bioimaging and fluorescence anti-counterfeiting were reviewed.Chapter 2:Green fluorescent N-CDs were prepared by one-step hydrothermal process to use catechol as carbon source and triethylenetetramine as nitrogen source.The structure and properties of the constructed N-CDs were studied in detail.The results show that the N-CDs have good photoluminescence properties and can be used for dual-functional sensing of Fe³⁺and ascorbic acid(AA).Fluorescence of N-CDs was quenched by Fe³⁺because Fe³⁺can form chelates with functional groups on the surface of N-CDs by static quenching mechanism.In addition,AA can effectively prevent the quenching of CDs because AA can reduce Fe³⁺to Fe²⁺,which can restore the fluorescence of CDs.N-CDs were label-free fluorescent nanoprobes for the determination of Fe³⁺and AA with the corresponding detection limits of 58.82 n M and 0.236?M,and the linear ranges from 25-200?M and 25-300?M,respectively.The constructed fluorescence sensor has been successfully applied for the analysis of Fe³⁺in tap water and AA in fresh fruit with satisfactory results.The prepared N-CDs have low toxicity and good biocompatibility,which can be used for cell imaging and sensing of Fe³⁺and AA in living cells,expanding the application range of N-CDs.Chapter 3:N,P-CDs were speedily prepared by acid-base neutralization reaction with phthalic acid as raw material,EDA as nitrogen dopant and concentrated H₃PO₄ as phosphorus dopant.This method is automatic without external heat treatment,and can rapidly synthesize a large number of N,P-CDs,avoiding high temperature,complex operation and long reaction time.N,P-CDs have excellent luminescent properties,which can be used as a label free multifunctional fluorescence sensing platform for Mn⁷⁺detection,temperature sensing and cell imaging.Based on the internal filtering effect(IFE),Mn⁷⁺can effectively quench fluorescence of N,P-CDs.N,P-CDs were successfully used for determination of Mn⁷⁺in various teas and Chinese herbal medicine.Moreover,in terms of their good biocompatibility and low cytotoxicity,N,P-CDs can be used for imaging and sensing Mn⁷⁺in living cell.In addition,the emission intensity changes of the sensor showed a linear and reversible response in the temperature range of 25?80?,with a the sensitivity of-1.79%?,which expands the application of CDs in multi-sensor.Chapter 4:N-CDs were synthesized by acid-base neutralization reaction with glucose as carbon source,ethylenediamine(EDA)and concentrated nitric acid as double nitrogen dopants.N-CDs had good antioxidant capacity,which the inhibitory concentration of DPPH(2,2-diphenyl-1-picrylhydrazyl)was significantly lower than that of AA.Moreover,MIC test demonstrated that N-CDs had satisfying antibacterial activity against S.aureus and E.coli.In addition,N-CDs possessed stable fluorescence properties in a wide range of p H and high tolerance to ionic strength with fluorescence quantum yield(QY)of 14.2%,which can be used as nanoprobes for the detection of quercetin.The fluorescence of N-CDs was quenched due to the electrostatic interaction between the amino group of N-CDs and the 3-hydroxy group of quercetin.They have been successfully applied to the determination of quercetin in human serum and urine.Chapter 5:Green-emissive N,S-doped carbon dots(N,S-CDs)with a high QY of 60%were synthesized by a facile hydrothermal approach using methyl blue as only raw material.The-NH-and-SO_x-groups of methyl blue were simultaneously used as nitrogen and sulfur co-dopant to dope into CDs.The prepared N,S-CDs have an extremely large Stokes shift(?130 nm)and excitation-independent fluorescence,which have been successfully used in multiple applications for H₂S sensing,bioimaging and anti-counterfeiting.Taking advantage of the excellent optical properties of N,S-CDs,they could act as a label-free nanoprobe for the detection of H₂S.Fluorescence of N,S-CDs could be significantly quenched by H₂S because of dynamic quenching,along with excellent selectivity toward H₂S in the range of 0.5-15?M with a detection limit of 46.8 n M.They were successfully applied for the determination of H₂S in actual samples.Additionally,the nanoprobe was extended to bioimaging in both living PC12 cells and zebrafish,and monitoring H₂S in live cells.Furthermore,N,S-CDs have been used to prepare highly fluorescent polymer films by incorporating N,S-CDs in polyvinyl alcohol(PVA).As-prepared N,S-CDs/PVA films show prominent dual-mode FL properties,implying that they are potential nanomaterials in the anti-counterfeiting field.