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

Abstract

As superparamagnetic nanoparticles capture new applications and markets, the flexibility andmodifications of these nanoparticles are increasingly important aspects. Therefore a series ofmagnetic polystyrene particles encapsulating magnetite nanoparticles (10–12 nm) in a hydrophobicpoly(styrene-co-acrylic acid) shell was synthesized by a three-step miniemulsion process. A high amount ofiron oxide was incorporated by this process (typically 30–40% (w/w)). As a secondreporter, a fluorescent dye was also integrated in order to obtain ‘dual reporter particles’.Finally, polymerization of the monomer styrene yielded nanoparticles in the range45–70 nm. By copolymerization of styrene with the hydrophilic acrylic acid, the amount ofcarboxyl groups on the surface was varied. The characterization of the latexes includeddynamic light scattering, transmission electron microscopy, surface charge and magneticmeasurements. For biomedical evaluation, the nanoparticles were incubated with differentcell types. The introduction of carboxyl groups on the particle surfaces enabled the uptakeof nanoparticles as demonstrated by the detection of the fluorescent signal by fluorescentactivated cell sorter (FACS) and laser scanning microscopy. The quantity of ironin the cells that is required for most biomedical applications (like detection bymagnetic resonance imaging) has to be significantly higher, as can be achievedby the uptake of magnetite encapsulated nanoparticles functionalized only withcarboxyl groups. A further increase of uptake can be accomplished by transfectionagents like poly-L-lysine or other positively charged polymers. This functionalitywas also engrafted into the surface of the nanoparticles by covalently couplinglysine to the carboxyl groups. The amount of iron that can be transfected waseven higher than with the nanoparticles with a transfection agent added andthis only physically adsorbed. Furthermore, the subcellular localization of thesenanoparticles was demonstrated to be clustered in endosomal compartments.