Imaging of intracellular behavior of polymeric nanoparticles in Staphylococcus epidermidis biofilms by slit-scanning confocal Raman microscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy

Abstract

In drug delivery systems employing polymeric nanoparticles, accurate delivery of drugs to target sites such as bacterial cells, cell tissues, and organelles is essential. In particular, when designing drug delivery systems for the treatment of the biofilm infections, evaluation of the interaction between polymeric nanoparticles and biofilm or bacterial cells using a simple technique is of significant importance. Here we develop two types of novel techniques for the biological imaging of the intracellular behavior of two types of polymeric nanoparticles, biodegradable chitosan-modified poly (dl-lactide-co-glycolide) (PLGA) nanoparticles and chitosan-modified polyvinyl caprolactam - polyvinyl acetate -polyethylene glycol graft copolymer (Soluplus®, Sol) nanoparticles, within a Staphylococcus epidermidis biofilm. As the first technique, Raman imaging of unstained biological materials using slit-scanning confocal Raman microscopy (unstained Raman imaging) was performed, and as the second, field-emission scanning electron microscopy with energy-dispersive X-ray spectroscopy analysis of biological materials labeled with quantum dots (SEM-QD imaging) was demonstrated. These analyses revealed differing localization of the respective nanoparticles within the biofilm in accordance with the specific interactions of PLGA nanoparticles and Sol nanoparticles with the biofilm. These novel techniques open the door to biological imaging and analyses with high spatial resolution, which will help to understand the efficacy of drug delivery to target materials.