Encapsulation of Nile Red in polypyrrole microvessels

Polymeric hollow structures are a popular topic in modern chemistry and materials science because of their potential importance in biomedical applications such as smart drug delivery systems. We report on the preparation of polypyrrole microvessels that are capable of encapsulating Nile Red, a solvatochromic dye that serves as a model of lipophilic drugs. Using a range of modern physicochemical methods including electron and optical microscopy, vibrational and fluorescence spectroscopy, and zeta potential measurements, we show that the dye can be encapsulated effectively through chemical polymerization of pyrrole onto p-xylene droplets that contain Nile Red. The fluorophore resides within the organic core of the microvessels but interacts with the polymer wall material (or pyrrole oligomers formed during polymerization) which is manifested as slower rotational dynamics and shorter fluorescence lifetime of the dye in comparison to bulk solvent. We also demonstrate release of the dye to the surrounding solution and show that this process is governed primarily by the miscibility of the organic core (p-xylene) with the external phase (solvent).