Preparation Of Near-Infrared Biomass Quantum Dots And Its Application

Carbon dots(expressed as Cdots)are also known as carbon quantum dots.It consists of a wide range of non-toxic carbon elements on the earth with a diameter of less than 10 nm.Due to its excellent fluorescent properties,good biocompatibility and low biotoxicity,it has attracted more and more attention from scientists and technicians.Carbon quantum dots have been used in biosensing,drug delivery,bioimaging,and cancer therapy.Carbon quantum dots synthesized from natural biomass are called biomass quantum dots.Due to their simple synthesis method,easy synthesis,low cost,wide range of raw materials,and better biocompatibility,Sense,drug transport,bioimaging and cancer treatment,have a wider application prospect.However,the maximum emission wavelengths of the currently reported biomass quantum dots are all less than 600 nm,which limits their application in in vivo imaging.Therefore,the preparation of biomass quantum dots for near-infrared fluorescence emission has become a major challenge in the development of carbon-based quantum dots.In order to cope with this challenge,three near-infrared biomass quantum dots were synthesized from cucumber,mint leaves and holly leaves,and used for Hg²⁺imaging in cells,ratio fluorescence imaging of survivin mRNA in cells and ratiometric fluorescence imaging for peroxynitrite in living organisms.The details are as follows:(1)A near-infrared fluorescence biomass quantum dots(C-BQDs)was prepared by solvothermal method using cucumber as raw material.The biomass quantum dots produces a strong fluorescence emission peak at 675 nm,and Hg²⁺can quench its fluorescence.Therefore,the biomass quantum dots can be used as a new fluorescent nano-probe for Hg²⁺detection.At the time of detection,the fluorescence intensity of the probe showed a good linear relationship with the concentration of Hg²⁺in the range of 0-110?mol/L,and the detection limit was 0.1?mol/L.The probe has good selectivity,and the common metal ions in the living body do not interfere with the detection of Hg²⁺.It is used for imaging Hg²⁺in living cells,and the fluorescence intensity of the cells gradually decreases as the concentration of Hg²⁺increases.(2)Using a mint leaf as a raw material,a near-infrared fluorescence biomass quantum dots(M-BQDs)was prepared.The maximum emission wavelength of the biomass quantum dots is at 670 nm,and the maximum absorption wavelength of the dye Dylight680(680 nm).There is a greater degree of overlap.To this end,this study first linked a single-stranded DNA to M-BQDs,then linked the dye Dylight680 to the nucleic acid aptamer of survivin mRNA,and linked the dye Dylight680 on the M-BQDs'surface by the principle of complementary base pairing.At this time,fluorescence resonance energy transfer occurs between M-BQDs and Dylight680,the fluorescence intensity of M-BQDs decreases,and the fluorescence intensity of Dylight680 increases.In the presence of survivin mRNA,Dylight680 sheds from the surface of M-BQDs due to the binding of survivin mRNA to its aptamer,resulting in a gradual decrease in the fluorescence intensity of Dylight680(maximum emission peak 720nm),a gradual increase in the fluorescence intensity of M-BQDs,and a fluorescence intensity ratio.The logarithm of(I_{670n m}/I_{720n m})and the concentration of survivin mRNA showed a good linear relationship in the range of 0-475 nmol/L,and the detection limit was 5.5 nmol/L.The imaging of survivin mRNA in Hela,MCF-7(tumor cells)and MCF-10A(normal cells)cells revealed that the ratio of the fluorescence intensity of survivin mRNA in tumor cells(I_{670n m}/I_{720n m})was significantly higher than that of the cells.It is indicated that the functionalized M-BQDs can be used as a fluorescent probe for the recognition of cancer cells and normal cells.At the same time,this study also explored the application of synthetic near-infrared fluorescent biomass quantum dots as photosensitizers for photodynamic therapy of tumor cells.The results show that the biomass masses can generate a large amount of reactive oxygen species under irradiation of 660 nm laser.After 5 min(200 mW/cm²)irradiation,the survival rate of cancer cells was less than 30%.(3)A near-infrared fluorescence biomass quantum dots(H-BQDs)is prepared using holly leaves as the raw material.The maximum emission wavelength of this biomass quantum dots is at 670 nm.Since the absorption spectrum of the dye Cy7 can effectively overlap with the emission spectrum of the synthesized biomass quantum dots,Cy7 is connected to the surface of H-BQDs by covalent coupling(H-BQDs-Cy7)as a peroxynitrite(ONOO^-)nanoprobe.Based on the principle of fluorescence resonance energy transfer,the fluorescence intensity of H-BQDs in the probe is decreases,and the intensity of Cy7 fluorescence(780 nm)is increases.When peroxynitrite(ONOO^-)is present,the molecular structure of dye Cy7 is destroyed,and its absorption undergoes blue shift,no longer effectively overlaps with the emission spectrum of H-BQDs,also means no fluorescence resonance occurs between the two of them.At this time,the fluorescence of Cy7(780 nm)gradually decreased,the fluorescence of H-BQDs gradually increased,and the logarithm of the fluorescence intensity ratio(I_670nm/I_{780 n m})and the concentration of ONOO-in the range of 0-15?mol/L.A good linear relationship is exhibited with a detection limit of 0.12?mol/L.The probe has good selectivity,and other common biologically active substances in the cell do not interfere with the detection of ONOO-.The ratiometric fluorescence imaging applied to exogenous and endogenous ONOO^-in RAW264.7 cells showed good imaging results.Based on the near-infrared fluorescence with good tissue penetrating ability,the nanoprobe has been used for ratiometric fluorescence imaging of endogenous ONOO^-in vivo,and ratio-fluorescence imaging is used to track the production of endogenous ONOO^-in situ.