Synthesis and biomedical applications of functionalized fluorescent and magnetic dual reporter nanoparticles as obtained in the miniemulsion process

As superparamagnetic nanoparticles capture new applications and markets, the flexibility and modifications of these nanoparticles are increasingly important aspects. Therefore a series of magnetic polystyrene particles encapsulating magnetite nanoparticles (10–12 nm) in a hydrophobic poly(styrene-co-acrylic acid) shell was synthesized by a three-step miniemulsion process. A high amount of iron oxide was incorporated by this process (typically 30–40% (w/w)). As a second reporter, a fluorescent dye was also integrated in order to obtain 'dual reporter particles'. Finally, polymerization of the monomer styrene yielded nanoparticles in the range 45–70 nm. By copolymerization of styrene with the hydrophilic acrylic acid, the amount of carboxyl groups on the surface was varied. The characterization of the latexes included dynamic light scattering, transmission electron microscopy, surface charge and magnetic measurements. For biomedical evaluation, the nanoparticles were incubated with different cell types. The introduction of carboxyl groups on the particle surfaces enabled the uptake of nanoparticles as demonstrated by the detection of the fluorescent signal by fluorescent activated cell sorter (FACS) and laser scanning microscopy. The quantity of iron in the cells that is required for most biomedical applications (like detection by magnetic resonance imaging) has to be significantly higher, as can be achieved by the uptake of magnetite encapsulated nanoparticles functionalized only with carboxyl groups. A further increase of uptake can be accomplished by transfection agents like poly-L-lysine or other positively charged polymers. This functionality was also engrafted into the surface of the nanoparticles by covalently coupling lysine to the carboxyl groups. The amount of iron that can be transfected was even higher than with the nanoparticles with a transfection agent added and this only physically adsorbed. Furthermore, the subcellular localization of these nanoparticles was demonstrated to be clustered in endosomal compartments.