Synthesis And Performance Of Carbon Dots For Nucleic Acid-Targeting Fluorescence Imaging And Photodynamic Therapy

Carbon dots(CDs),as a new type of zero-dimensional carbon nanomaterial,is generally less than 10 nm.Depending on the excellent optical properties,CDs have attracted extensive attention in the fields of biological imaging and tumor therapy.Moreover,CDs exhibit better biocompatibility than inorganic nanomaterials,as well as simple preparation and low cost compared to organic fluorescent probes.However,the absorption and emission wavelengths of most CDs mainly located within 400-500 nm,which are easily interfered by background fluorescence in bioimaging.Besides,most of CDs are lack of specific capability,such as targeting.In this thesis,the correlation between molecular structure of carbon source and performance of CDs are investigated,which is applied in adjusting the emission of CDs from visible to near infrared region.Furthermore,doping heteroatom(e.g.nitrogen,selenium and iodine),CDs can be invested nucleic acid-targeting and photodynamic properties.Therefore,the development of near infrared photodynamic CDs provides a new strategy for the integration of cancer diagnosis and treatment.The doping of nitrogen and other elements in CDs was helpful to regulate their properties and functions.In the bottom-up synthesis,the contents of graphite nitrogen in CDs changed by using carbon source with primary amine,secondary amine and tertiary amine,respectively.And the graphite nitrogen contents affected the energy gap of CDs obviously,resulting in the adjustable emission from visible to near infrared range.Based on the above strategy,N-0-CDs,N-1-CDs,N-2-CDs,N-3-CDs and N-4-CDs were prepared by solvothermal method.The experimental results showed the the maximum absorption/emission wavelengths of above CDs gradually redshifted(461/527,520/543,545/566,572/590 and 650/676 nm)along with the increase of graphite nitrogen contents obviously(10.6%→30.1%).The cell image,nucleic acid titration and nucleic acid digestion experiments results proved above N-CDs could selectively bind nucleic acid by hydrogen bond and electrostatic interaction,especially to RNA preferentially.The detection limit of N-2-CDs for RNA was 65.8 ng/mL,which could be applied in a real-time detection of intracellular RNA.Inspired of the heavy atom effect,selenium(Se)was introduced in the carbon source together with nitrogen to prepare Se/N-CDs.As expected,Se/N-CDs exhibited a capability of photodynamic therapy with a 1O2 yield of 10.6%.The cell viability decreased gradually(100%→20%)with the increase of Se/N-CDs concentration(0→7.5μg/mL)in photodynamic tests.The Se/N-CDs could preferentially bind RNA,which is confirmed by the intracellular nucleic acid digestion and isothermal titration microcalorimetry.Moreover,RNA could be used as carrier to deliver Se/N-CDs nearby the nucleus,wherein the 1O2 was produced to damage nuclear membrane under light illumination.Therefore,a large amount of Se/N-CDs penetrated into the nucleus to kill cancer cells with efficiency.Base on above results,the "targeting structure-inheritance" strategy was supposed to delivery from carbon source to CDs.Therefore,the QN-1-CDs,QN-Cl-CDs and QN-I-CDs were synthesized by using quinoline structure and its derivatives,which were most common units in the structures of nucleic acid probes.And all these CDs possessed near infrared absorption and emission.The SYTO? RNA SelectTM re-staining,nucleic acid digestion assay and fluorescence response assay of nucleic acid confirmed that the above CDs could effectively"inherit" nucleic acid-targeting properties from carbon sources.Among them,the doping of micro iodine in QN-I-CDs effectively improved its photodynamic performance,and the cell survival rate was less than 20%after light irradiation.The folic acid(FA)-modified liposomes QN-I-CDs@FA were prepared,which could be targeted to tumor tissues,and thus effectively inhibiting tumor growth.