Preparation And Performance Characterization Of Fluorescent Magnetic Composite Nanoparticles

With the development of the nanotechnology, magnetic matericals and luminescentquantum dots have been widely applied in the field of biomedicine because of their smartperformance and character. We can synthesize magnetic and fluorescent multifunctionalnanocomposite, which combines magnetic and fluorescent as well as integrates separation andlabel performance through a series of physical and chemical reaction processes. Themultifunctional nanocomposite material can be used as a fluorescent probe, but also has agood magnetic response. On this basis, in this paper, we use the nuclear magnetic resonancecontrast agent superparamagnetic Fe₃O₄as magnetic nucleus to provide magnetism, and useZnSe@ZnS core-shell structure quantum dots with color-adjustable and high luminousefficiency for fluorescence application. Finally, we obtain magnetic fluorescent compositenanoparticles. Meanwile, we combine the magnetic nanoparticles with antitumor drugscovered by natural polymer chitosan to get drug-loading magnetic chitosan microspheres.This new type of composite nanomaterials not only expand its potential applications inbiomedical, but also effectively overcome the drawbacks of magnetic nanoparticles andquantum dots, such as the susceptibleness to oxidation of Fe₃O₄nanoparticles, environmentsensitiveness and biological toxicity of quantum dots. Thus, it allows us to further expand itspotential application and utilization scope.In this paper, nanometer-sized ZnSe quantum dots, glutathione asstabilizer, was preparedby co-precipitation method. The produced ZnSe quantum dots showed high luminousintensity, water-soluble and stable properties. The ZnSe nanocrystals were characterized byX-ray diffraction （XRD） analysis, transmission electron microscopy （TEM） analysis, UV-visabsorption spectrum and fluorescence spectrum analysis in order to get the best preparationtechnology parameters. The result shew that the best luminescence property were attainedwhen precursors molar ratio of Zn/Se/GSH was fixed at1:0.4:1.2, with tempetature at90°Cand the pH value of12for1hour. Under the above reaction condition, the ZnSe quantum dotsshew best luminescent and stable properties. Meanwhile, we found that natural lightirradiation was beneficial to enhance the fluorescence intensity and quantum yield. On the basis of ZnSe quantum dots and via the epitaxial growth method, we gotZnSe@ZnS core-shell quantum dots by depositing a broad band gap layer ZnS on the surfaceof ZnSe quantum dots contributing to the thiourea decomposition at high temperature. Inaddition, we investigated the different reaction parameter effect on the luminous performanceof core-shell structure ZnSe@ZnS quantum dots, such as pH values, reaction times, etc. Theresult shew that the ZnSe@ZnS core-shell quantum dots had a narrow particle sizedistribution and the average diameter was3.6nm. Due to the quantum size effect, quantumdots absorption spectrum and fluorescence spectrum occured obviously red shift. It wasobviously beneficial for the combination of Zn2+and S2-ions when the temperature at100°Cand pH=10.5for2hours. Thus we could get ZnSe@ZnS core-shell quantum dots with bestluminescence properties. After the modifition of ZnS, the quantum yield of ZnSe@ZnSquantum dots increased dramatically, from23%climbing to62.8%. Moreover, the core-shellstructure of ZnSe@ZnS quantum dots also significantly extended fluorescence lifetime andhad a good fluorescent stability.Fe₃O₄magnetic nanoparticles prepared by solvothermal method, which had a goodcrystallization and monodispersity. The average diameter of magnetic nanoparticles was about10-15nm. The aggregation phenomenon of Fe₃O₄magnetic nanoparticles were serious for thesynthetic samples, so we carried out surface modification by the effect of hydrochloric acid.Results shew that the Fe₃O₄-H3O+magnetic nanoparticles modified by hydrochloric acid hadgood dispersibility in water solution, the dispersion of nanoparticles was best when theconcentration of hydrochloric acid was0.03M. Moreover, we studied the possible mechanismby the diffusion bilayer on nanoparticles, and we found that magnetic nanoparticles still hadgood superparamagnetism at room temperature.In order to obtain the magnetic fluorescent composite nanoparticles, ZnSe@ZnSquantum dots will be introduced into the surface of the Fe₃O₄magnetic nanoparticles obtainedusing chemical bonding mechanism and finally get the magnetic fluorescent nanocompositeparticles Fe₃O₄-QDs. Firstly, Fe₃O₄@SiO₂nanoparticle would be modified byAPTES（3-aminopropyl triethoxysilane）, then obtained amino-modified Fe₃O₄@SiO₂core-shell nanoparticles, and combined with ZnSe@ZnS quantum dots through the activatorreagent. The structure and luminescence performance of composite nanoparticles were charactered by X-ray diffraction （XRD） analysis, transmission electron microscopy （TEM）,UV-vis absorption spectrum and fluorescence spectrum. The results demonstated that theintensity of fluorescence and saturated magnetization of composite particle Fe₃O₄-QDsexperienced a slightly decrease, but it displayed a superparamagnetic pattern at roomtemperature as well.The natural macromolecules chitosan is often used as a carrier of anticancer drugs. Inthis paper, chitosan polymer was capped during the combination process of magneticnanoparticles with5-Fu anticancer drug （a common anticancer）. What’s more, we investigatedthe drug loading and sustained release effect of drug-loading magnetic chitosan microspheresin depth. At the same time, we examined the amount of crosslinking agent and crosslinkingtime during experiments on the morphology and release properties of drug-loadedmicrospheres. Through the establishment of standard absorption curve of5-Fu, we measureddrug loading and encapsulation efficiency of the drug carrier. The results depicted that thedrug-loaded microspheres at different pH environment had excellent sustained release effect;the drug carrier had the fastest release rate when the pH value was2. Moreover, the releaserate of drug carrying microsphere was close to100%after the reaction with24h at pH=2.The microsphere drug loading was S1=8.8%and encapsulation efficiency was S2=41.1%. Itsrelease rate became much slower with the increase of the amount of crosslinking agent andthe rising feeding molar ratio of n（CS）:n（5-Fu）), which indicated that the water-solublechitosan microspheres is a superior sustained-release material, widely applied in potentialanti-tumor therapy.