Preparation And Properties Of Magnetic Fluorescent Nanostructured Particles

Due to the combination of magnetic and fluorescent properties, multifunctional magnetic fluorescent nanostructured particle systems have attracted significant attention as ideal candidates for various biomedical applications, such as bioseparation, targeted drug delivery, multimodal imaging and biological detecting. As a simple and general method, self-assembly strategy has been adopted to construct magneto-optical nanosystems with different compostitions and combinations. Based on the weak interparticle forces, magnetofluorescent nanocomposites can be obtained utilizing the presynthesized magnetic and fluorescent subunits, and their structures and properties can be conveniently tailored.In this work, magnetite nanoparticles were initially synthesized through the thermal decomposition method, and core-shell CdSe/CdS/ZnS quantum dots (QDs) were prepared via successive ion layer adsorption and reaction (SILAR) technique.3-Aminopropyltriethoxysilanes (APS) were covalently attached to the surface of magnetite nanoparticles and the amino-silane coated magnetic nanoparticles were subsequently protonated in order to render the modified magnetic nanoparticles cationic. Water-soluble QDs passivated with mercaptopropionic acid (MPA) were acquired by ligand exchange and then were deprotonated by NaOH. Based on electrostatic attraction, hydrophilic magnetic fluorescent nanocomposites were assembled from the positively charged magnetic nanoparticles and negatively charged QDs. The analysis results revealed that the hydrophilic magnetic fluorescent nanoparticles had a size distribution in the range of20-30nm. The product had a saturation magnetization value of14.0emu-g~-1with superparamagnetic behavior at room temperature. Besides, the hydrophilic magnetic fluorescent nanoparticles showed high luminescence intensities under illumination.Magnetite nanoparticles were initially coated by3-mercaptopropylthrimethoxy-silanes (MPS). After that, bifunctional magnetic fluorescent nanoparticles were achieved by directly assembling hydrophobic QDs onto the surface of magnetic nanoparticles through the strong coordination interactions between zinc atoms and thiol groups. The analytical results demonstrated that QDs were densely attached on the magnetic cores, and the ultimate size of the product was around40nm. The resultant magnetofluorescent bifunctional nanoparticles had a saturation magnetization value of16.8emu-g~-l with superparamagnetic characteristics at room temperature. In addition, bright red luminescence could be seen from the fluorescence microscopy image, except for a slight decrease of the photoluminescence quantum yield in contrast to that of the original QDs.Hollow magnetic nanobowls were fabricated in oil-in-water emulsion system immediated by anionic polyelectrolytes polyepoxysuccinic acid sodium salt (PESA). Meanwhile, original QDs were transferred into aqueous phase by densely positively charged polyethyleneimine. Utilizing the as-prepared magnetic nanobowls and PEI-stabilized QDs as building blocks, magnetofluorescent nanobowls were finally fabricated through the intense electrostatic forces. Transmission electron microscopy (TEM) images showed that the magnetofluorescent nanobowls enlarged to135nm in diameter with several layers of QDs. Moreover, the magnetofluorescent nanobowls also exhibited rapid magnetic response and well-kept luminescent properties.