| Carbon dots(CDs)is a new member of the carbon family with a size of less than 10 nm.In the past ten years,CDs have been favored because of their unique physical and chemical properties,such as cheap and easy to synthesize methods,easy surface modification,excellent photoluminescence,good water solubility,and low toxicity.Given these advantages,CDs have been widely used in many research fields,such as photocatalytic reactions,drug gene delivery systems,in vitro and in vivo bioimaging,chemical and biosensing,and photodynamic and photothermal therapy.There are many potential problems in the current methods for preparing CDs,such as environmental pollution,high consumption and harsh synthetic conditions.It is a trend to use eco-friendly precursors to prepare CDs as much as possible.However,the fluorescence quantum yield(QY)of CDs synthesized by most green strategies is relatively low.QY is extremely important for fluorescent biological imaging and biosensing.In addition,doping heteroatoms can affect the electron level and the overall electric distribution,which is considered to be an effective measure to adjust the fluorescence performance of CDs.In view of the above problems,in this paper,four types of functional CDs with excellent optical properties are achieved by hydrothermal and microwave treatment of biomass,the combination of biomass and chemical materials as carbon and nitrogen sources,as well as sulfur and phosphorus atoms with larger radii,which are characterized by the existing technology,and applied to chemical,biological sensing and drug delivery researches.The main contents are demonstrated as follows:1.carbon dots(CDs)with high fluorescence quantum yield(14.8%)were prepared by using cotton as a carbon source through combining pyrolysis and microwave treatment.The synthesized spherical fluorescent CDs emit blue fluorescence with an average particle diameter of 4.9±0.10 nm,showing good dispersibility,excellent biocompatibility,low toxicity,and good stability.Thefabricated CDs have been successfully applied to Fe3+ sensing,multicolor cellular imaging and patterning.The linear range of Fe3+ ion detection is50-10000 n M with the detection limit of 27 n M,which provides a new platform for highly sensitive detection of Fe3+ ions.In addition,human cervical squamous cell carcinoma cells(A193)were used as models for multicolor cell imaging.Confocal microscopy showed that CDs can cross the cell membrane into the cytoplasm and nucleus,indicating that CDs can be used as excellent biomedical probes.Besides,the successful drawing of multicolor fluorescent patterns implied that CDs have a good application prospect in the field of anti-counterfeiting.2.Nitrogen-doped carbon dots(N-CDs)were synthesized using pigskin as a precursor through a simple and environmentally friendly strategy.The prepared N-CDs showed great advantages,including high fluorescence quantum yield(24.1%),excellent biocompatibility,low toxicity and satisfactory chemical stability.Relying on these excellent characteristics,the N-CDs have been successfully used for multicolor cell imaging.In addition,N-CDs have a strong response to Co2+ ions to cause fluorescence quenching,indicating that N-CDs can selectively detect Co2+ with a detection limit of0.68 μM.Further applications have been extended to the fluorescence sensing of Co2+ ions in living cells.3.Hydrothermal treatment of the mixture of frozen tofu,ethylenediamine and phosphoric acid successfully synthesized high yield(64%)of nitrogen and phosphorus co-doped fluorescent carbon dots(N,P-CDs).The obtained N,P-CDs showed low toxicity,and high biocompatibility.The N,P-CDs can selectively and sensitively detect Co2+with a detection limit of 58 n M based on Co2+ effectively quenching the fluorescence of N,P-CDs,which is 8.5 times low than that of the above N-CDs.In view of the basic principle of complexation of Co2+ and EDTA,an“off-on” fluorescence sensing method was developed,which can quickly and sensitively detect EDTA with a detection limit of 98 n M,achieving Co2+ andEDTA are detected simultaneously on the same nanoprobe platform.Meanwhile,multicolor bioimaging in vitro and in vitro was applied in cells and zebrafish.More excitingly,zebrafish internal circulation experiments have demonstrated that the N,P-CDs is of superior biocompatibility and good efflux metabolism ability.Therefore,this high-yield N,P-CDs is expected to be as a candidate for bioimaging and intelligent drug delivery.4.Here,innovative nitrogen and sulfur co-doped bright orange fluorescent carbon dots(N,S-CDs)are easily obtained using methyl-β-cyclodextrin(Me-β-CD)and methylene blue as original materials via the hydrothermal method.The prepared N,S-CDs show excellent fluorescence stability in a wide p H range and external anions and cations,while its fluorescence can be quenched by folic acid(FA),and the fluorescence quenching mechanism is static quenching.The detection limit is0.85 n M.In addition,N,S-CDs have superior photobleaching resistance compared to commercially available green fluorescent probes fluorescein isothiocyanate(FITC).Biological imaging of N,S-CDs in zebrafish larvae has shown that they can be used as excellent candidates for in vivo imaging and tracing.Interestingly,through physical adsorption,the positively charged N,S-CDs exhibited the loading capacity of the anti-tumor drug mitoxantrone(MTO)and obtained the combination of tracking and treatment of fluorescent nanopharmaceutical systems(CDs-MTO).These results show that N,S-CDs is a promising luminescent material and can be used as a fluorescent biomarker for non-fluorescent drugs,in vivo imaging and FA sensing.Through the above researches,it provides a theoretical basis for the green synthetic high-fluorescence CDs for chemical,biological sensing,and drug delivery. |
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