Preparation Of Carbon Dots-based Polyelectrolyte Complexes Nano-Delivery Systems For Imaging

Carbon dots(CDs),as a new type of fluorescent nano-materials,are gradually become a hot topic in the field of biomedicine. It has excellent performance in the field of bio-optical imaging such as stable fluorescence properties,tunable emission wavelength,good water solubility,biocompatibility,low toxicity and so on.In recent years nano-formulation has been widely used in the field of food and drug with the development of nanotechnology.And the research of imageable nano-formulations has become the focus in the feild as bio-imaging technology has been matureing over recent years.Thus,the synthesis of excellent fluorescent carbon dots for imageable nano-formulations has important significance.This article synthesized fluorescent carbon dots by hydrothermal and modified its surface by polyethyleneimine.By direct embedding the CDs-PEI in carrageenan-chitosan polyelectrolyte nanoparticles,the nano-delivery systems has got visual function.Then the dispersion,stability and carrying capacity of the systems has been discussed.Finally cell cytotoxicity and cell imaging of the systems were studied.The main research contents and results are as follows:The water soluble carbon dots were prepared by hydrothermal reaction with arabinose and casein phosphopeptides,the optimum reaction temperature is 200?,the best time is 7 h,the best p H value is 9,the optimal degree of filling is 60%,the optimal proportion of arabinose and casein phosphopeptides is 0.32%:0.2%(w/v), in this condition the quantum yield of the carbon dots is 11.06%.Transmission electron microscopy,ultraviolet visible absorption spectroscopy,fluorescence spectroscopy and infrared spectroscopy and X-ray diffraction were used to characterize the particle size,absorption spectra,luminescence properties and surface groups of carbon dots.The PL intensity changes in the presence of representative metal ions under the same conditions were investigated to evaluate the selectivity of the carbon dots.The results showed that the average particle size of the fluorescent carbon dots is 4.62 nm and its maximum absorption wavelength is 281 nm.The XRD peak is about 21°.The fluorescent carbon dots could emit bright fluorescence in the ultraviolet light with maximum emission wavelength of 414 nm,the fluorescence emission spectrum is redshift with the increase of the excitation wavelength.The carbon dots have good water solubility,-COOH,-NH2 and-OH groups are on the surface of the carbon dots,it has excellent performance,but tremendous PL intensity decrease was observed by addition of Cu2+ and Fe3+.To improve their fluorescence property and functionalize them with amino-group,the bare carbon dots were modified by PEI then,the optimal reaction conditions were studied.In the water bath conditions,the optimum reaction time is4 h,the best temperature is 70?,the optimal PEI(20%)dosage is 6%(v/v).The modified carbon dots were characterized by FTIR,XRD,UV-Vis,FL spectrum.FTIR show the emergence of shock amide peak at 1630 cm-1,there occurs a C-N stretching vibration peak near 1427 cm-1,1346 cm-1 and 3419 cm-1 appeared the characteristic absorption peaks of-NH2.The XRD peaks appeared sharp crystallization peak at 17°.The UV maximum absorption wavelength is 214 nm.The maximum PL intensity excitation wavelength is 360 nm,the maximum emission wavelength is near 426 nm.And the quantum yield of the modified carbon dots is 30.14%.Study on the embedding and slow-releasing capability of PEI modified carbon dots(CDs-PEI)of different anionic polysaccharides,showed that carrageenan is the best choice.Chitosan and carrageenan were chosen as polycation and polyanion respectively to prepare polyelectrolyte composite of nano drug delivery systems by electrolyte self-assembly,the optimal reaction conditions of nano-delivery systems were: polyelectrolyte concentration is 0.1%,chitosan:carrageenan is 10:11,and p H is5.0,in that condition the composite particle size distribution is most concentrated,the average particle size is about 400 nm,and the polydispersion coefficient of the nano complexes is 0.3 or less.The study results on physical and chemical properties of the nanoparticles drug delivery system show that the system has good carrying capacity,excellent dispersion and storage stability.Embedding carbon dots and carrying curcumin had no significant effect on the stability of the system.Results showed that the average particle size of the system is around 400 nm and the PDI values is less than 0.3,the encapsulation efficiency of curcumin is between 60%~70%,and the solubility of the curcumin is up to 50 ?g/m L or more.FTIR of this prepared polyelectrolyte complexes nanoparticles drug delivery system(CDs-PEI@PEC)showed that CDs-PEI and curcumin is embedded in by intermolecular forces inside the complex.The cell cytotoxicity of the CDs-PEI@PEC nanoparticles were studied by MTT assay.Cytotoxicity results show,CDs-PEI@PEC(CDs-PEI,300?g/m L) showed very low cytotoxicity when the concentration was less than 1.50 mg/m L.Cell imaging results demonstrated that the cells cultured with the nanoparticles was clearly showed bright fluorescence under 405 nm laser irradiation,and the nanoparticles were intake by endocytosis of murine macrophage RAW 264.7.Further analysis showed that the visual delivery systems mainly through the excitation-emission fluorescence properties of CDs-PEI.