Synthesis and electron microscopic analysis of the self-assembly of polymer and ferritin core-shell structures

Self-assembly of poly(4-vinylpyridine) (P4VP) and ferritin produced a spherical core-shell structure, which was analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In particular, for better understanding, the organization of such core-shell nanostructures, an optimal protocol for preparation of TEM thin sectioning of ferritin-P4VP composites, was developed. It entails fixing the ferritin-P4VP complex with 2.5% glutaraldehyde and infiltrating it with a mixture of acetone/resin while omitting the OsO₄ postfixation and ethanol dehydration steps of the conventional protocol. Using this method, a round-shaped thin section structure with unevenly distributed dark and white components was observed. The dark component from the thin section structure was determined to contain ferritin by energy-filtered TEM imaging and iron element mapping, whereas the white part was identified as P4VP by its energy dispersive X-ray spectroscopy (EDS) spectrum.