Multifunctional Magnetic-Fluorescent Nanocomposites for Biomedical Applications

Currently, the drugs that are consumed affect both the pathological and normal cells causing formidable side-effects and slow recovery. Therefore excess dosage is needed as there is no system to guide the drugs to the pathological cells. In order to rectify this problem, multi-component nanoparticles for targeted drug delivery (TDD) can be made that feature magnetic nanoparticles with superparamagnetic properties for transport, semiconductor quantum dots with high luminescence as biolables and silica coating for stability and high drug loading capacity. Particles smaller than 10 nm are cleared by kidneys and larger than 200 nm by reticuloendothelial system (RES). Caveolae mediated endocytosis is a major pathway for cell internalisation for endothelial cells, smooth muscle cells and fibroblasts. Caveolae membrane invaginations lie in a size range of 50-80 nm. So it is essential that the nanoparticles lie in this size range. In this study, iron oxide (Fe3O4) magnetic nanoparticles (MNPs) were synthesised using coprecipitation method in aqueous solvent (ø = 5.7 ± 0.5 nm, >15 mg/ml) coated with polyacrylic acid (PAA) and thermal decomposition method in organic solvent (ø = 6.1 ± 0.7 nm, 35mg/ml) coated with cetyltriammonium bromide (CTAB). Both these methods delivered MNPs with narrow size distribution, which were shown to be consistent after measuring by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) techniques. The Dynamic light scattering (DLS) technique showed slightly larger size as it measures hydrodynamic size (polymer inclusive) rather than just particle size. Solubility of both the MNPs has been good in water. A new synthesis method for silica resulted in solid spherical nanoparticles (ø = 23.07 ± 2.13 nm). This very technique was used to encapsulate the Fe3O4 MNPs with equal concentration = 35mg/ml. PAA coated MNPs were not encapsulated by the solid silica nanoparticles and formed aggregated clusters. However, the CTAB coated MNPs were encapsulated in silica shell with the best yield of >80% when 0.3 g of CTAB and 2 ml of iron oxide with an average size of 45.3 nm ± 4.3 nm. Fe3O4@SiO2 synthesised by using 3ml of 35 mg/ml MNPs formed particles within a size range of 62-65 nm, whereas those synthesised using 2ml of 35mg/ml MNPs formed particles within a size range of 44-47 nm. Thioglycolic acid (TGA) coated CdTe quantum dots synthesised by coprecipitation method in aqueous solution had a zinc blend cubic structure which formed an intermediate between CdTe and CdS due to excess thiol groups. The average size of these particles was about 3 nm. The highest quantum yield (QY) of 19.7% was noticed between pH 7 and 8. These nanoparticles did show red shift in photoluminescence (PL) and adsorption peaks depending on the synthesis time and also the pH. However, these QDs were aggregated on the silica meshwork, which was confirmed by the x-ray photoelectron spectrometry (XPS) technique. The PL of these nanoparticles was completely quenched. The formation of spherical silica nanoparticles was obstructed due to the electrostatic interaction between TGA, lysine, and CTAB. With the commercial CdSe/ZnS QDs, the PL intensity dropped once these particles were transferred to the water phase using CTAB surfactant. These QDs primarily aggregated in the aqueous solution separately from the silica nanoparticles, which in turn reduced their numbers on the spherical silica nanoparticles. The amount of these QDs was very low such that the reduced PL intensity with red shift feature was attributed to the aggregated QDs rather than the QDs on the silica nanoparticles. The XPS technique did not reveal any presence of QDs on the silica nanoparticles