Investigation of nanoparticle distribution inside formed microparticles using Quantum Dots

Due to their unique fluorescence properties (e.g. tuneable emission spectra, bright and stable fluorescence), quantum dots show great promise for biological and pharmaceutical research, providing ideal probes to evaluate the distribution of nanoparticles for different applications. In this study quantum dots with customized surface properties, like hydrophobic and hydrophilic coatings, were embedded in microspheres made of biodegradable polymers. The aim was to investigate the influence of surface properties on the encapsulation process and the characteristics of the obtained particles. To produce the microparticles, the established and frequently used methods of solvent evaporation and solvent extraction were used with varying processing parameters, e.g. the organic polymer solvent, concentration of emulsion stabilizer (PVA) and applied temperature. Additionally, two polymers were used to prepare the microparticles, the lipophilic poly(DL-lactide-co-glycolide) and the partially hydrophilic block copolymer methoxypoly(ethylene glycol)-co-poly(DL-lactide). The obtained particles were characterized with regard to their size, morphology, the encapsulation efficacy and the quantum yield inside the particles. Using confocal laser scanning microscopy and electron microscopy, the spatial distribution within the formed polymeric matrix was analyzed. In future, nanosized quantum dots provide a useful tool to localize crystals inside microparticles and to trace release in pharmaceutical delivery systems.