Polymer Nanoparticles Microenvironment: Using Photophysical Probes to Investigate Internal Porosity and Polarity

The objective of this work was to probe the internal morphology, porosity, and polarity of conjugated polymer poly[9,9-di(2-ethylhexyl)-fluorenyl-2,7-diyl] (PF2/6) nanoparticles (NPs) to assess their feasibility as drug-delivery vehicles. To this end, conjugated polymer PF2/6 NPs of varying size were prepared using a reprecipitation method; size was controlled using different injection speed and agitation power. Dynamic light scattering and fluorescence-based maximum entropy method Fluorescence correlation spectroscopy measurements indicate that the hydrodynamic diameters of NPs increase from method 1 to method 3 (40, 60, 80 nm, respectively). However, atomic force microscopy measurements indicate that NPs shrink to ca. 10 nm upon drying. Further experiments suggest that this occurs due to NP porosity, which increases with increasing hydrodynamic size as progressively more water becomes trapped within the microenvironment of the NP. Single NP fluorescence images show that fluorescence brightness for NPs o...