Uptake and intracellular fate of polymeric nanoparticles studied by light and electron microscopy : from labeling strategies for polymers towards a correlative microscopy approach

In nanomedicine, synthetic nanoscale objects are utilized as vectors to transfer pharmaceutically active compounds into partiular cell types, where they are released in a controlled manner to address intracellular organelles selectively. Polymeric nanomaterials, which represent a material class of tremendous interest for drug delivery, are in focus of this present thesis. In order to study their mode-of-action and deduce comprehensive concepts of particle-cell interactions, high-performance imaging techniques represent a particularly valuable investigation platform, since they provide a direct insight into cellular uptake mechanisms as well as their intracellular distribution. For this reason, the present thesis pursues the implementation of two suitable imaging techniques providing information on a high-resolution level, i.e. fluorescence microscopy (FM) as well as transmission electron microscopy (TEM). In this context, the utilization of carefully selected labeling strategies renders FM a powerful technique, which enables the unambiguous identification of the particles within their intracellular environment with an appropriate image contrast. Nonetheless, this method suffers from a poor resolution, so that individual particles cannot be sufficiently visualized. TEM, on the contrary, exhibits a resolution far beyond the particle size; however, polymeric nanomaterials do not show an appropriate image contrast alongside the cellular interior, which is a direct result of their similar electron contrasts. In this thesis, the implementation of both microscopy approaches into uptake studies is in focus, and the informative value of both methods is discussed. The advantages and drawbacks of both methods are pointed out, and it is illustrated that a comparison or even a correlation of both methods is highly beneficial to obtain a more complete insight. This discussion comprises as well different labeling strategies and experimental challenges.