Preparation And Biological Application Of Tunable Multicolor Photoluminescent Carbon Dots

As one of the most abundant elements in nature,carbon has been widely used in a large number of nanomaterials.As a kind of zero-dimensional spherical carbon-based nanomaterial with particle size less than 10 nm,carbon dots(CDs)have been used in energy catalysis,fluorescence arrays,bioimaging,nanomedicine and other fields due to their excellent water-solubility,optical stability,low toxicity and bio-compatibility.However,at present,the fluorescent color of CDs is still mainly blue,and there are some shortcomings,such as single color of fluorescence and weak luminescence in the long-wave region.In the field of biological applications,most CDs are not targeted for bioimaging.In terms of bacteriostatic applications,the specific bacteriostasis mechanism is not clear.Therefore,this paper focuses on the preparation and biological application of tunable multicolor photoluminescent CDs.Three kinds of tunable multicolor photoluminescent CDs have been successfully prepared and applied to the in vitro cell imaging and bacteriostasis research.The detail research contents consist of the following three parts:1.Preparation and analysis of three tunable multicolor photoluminescent carbon dots.Natural honey-based carbon nanodots(HCDs)were purified by dialysis using natural honey as source,and the fluorescence quantum yield was 8.3%,by tuning the excitation wavelength,fluorescence covering the whole visible region can be obtained.Nitrogen and phosphorus co-doped carbon quantum dots(N,P-CQDs)were synthesized by using microwave-assisted method with mango peel as carbon source and phosphoric acid solution as medium.The fluorescence quantum yield was 14.3%,when the excitation wavelength was tuned in the range of 330 nm to 470 nm,fluorescence in the blue to red region can be obtained.Nitrogen and fluorine co-doped carbon quantum dots(N,F-CQDs)were prepared by one-step hydrothermal method using o-phenylenediamine and 2,3,5,6-tetrafluoroterephthalic acid as carbon sources and anhydrous ethanol as solvent.The fluorescence quantum yield was 29.6%,when the excitation wavelength was gradually increased from 340 nm to 500 nm,the emission spectrum can cover the whole visible region.Through a series of characterizations such as TEM,XRD,Raman spectroscopy,XPS,FT-IR,UV-Vis spectroscopy,fluorescence spectroscopy and Zeta potential,the particle size,morphology and structure characteristics,element composition,potential change and optical properties of the three CDs were characterized and analyzed.Compared with most blue-emitting CDs,it has been proved to have excellent tunable multicolor photoluminescent properties.The effects on element doping,photoluminescent mechanism and structural model were preliminarily analyzed and discussed by comparison.2.Cell multicolor imaging application study of three carbon dots.Three tunable multicolor photoluminescent CDs were used for in vitro cell imaging study of U-2 OS cells,HT-29 cells,and HeLa cells.The standard MTT method was used to prove that all three CDs have less cytotoxicity in vitro.Laser confocal imaging analysis shows that three CDs have excellent tunable multicolor photoluminescent properties,bio-compatibility and light stability.It was found that HCDs,N,P-CQDs can be distributed in most parts of cells and belonged to non-selective fluorescence labeling.However,N,F-CQDs can target specific protein sites of HeLa cells without passing through the nuclear membrane.It is indicated that all three CDs are suitable for cell imaging of living cells,and N,F-CQDs have targeted labeling properties for the cytoskeleton of HeLa cells.3.Study on the antibacterial activity and mechanism of N,P-CQDs and N,FCQDs.E.coli and S.aureus were used as experimental models of Gram-negative bacteria and Gram-positive bacteria,respectively.The growth curve and the platecoated viable counts showed that the two negatively charged N,P-CQDs and N,F-CQDs had good bacteriostatic activity.Scanning electron microscopy and laser confocal imaging were used to observe the binding of CQDs to bacteria.Finally,the expression of strain-related genes was determined by RT-PCR.It was proved that two CQDs could inhibit the growth and metabolism of E.coli mainly by inhibiting the expression of RNA polymerase,inhibiting the carbon metabolism and sugar transformation of bacteria,inhibiting cell division,inhibiting its asexual dichotomy,and inhibiting the growth and metabolism of bacteria.For S.aureus,it mainly inhibits the formation of cell membrane and biofilm,quorum sensing system,DNA replication and cell division,so as to obstruct the expression of virulence factors,destroy the infection behavior and promote cell lysis.