Self-assembly process of soft ferritin-PNIPAAm conjugate bionanoparticles at polar-apolar interfaces

We describe an in-depth investigation on the dynamics and assembly behavior at polar-apolar interfaces of ferritin-PNIPAAm conjugates (poly-N-isopropylacrylamide). The stabilization of oil-water interfaces by the modified ferritin was investigated by dynamic surface tension measurements and compared to the individual components of the bionanoparticle conjugate, namely, unmodified ferritin and pure PNIMAAm of similar molecular weight. It was found that the modified ferritin, even at a low particle concentration, rapidly reduces the interfacial tension. The difference in interfacial stabilization was also shown by cryo-scanning electron microscopy and scanning force microscopy, which displayed very different morphologies at the polar-apolar interface for the unmodified ferritin, pure PNIPAAm, and the ferritin-PNIPAAm conjugate, respectively. The self-assembly of the ferritin-PNIPAAm was further analyzed by cryo-transmission electron microscopy and fluorescence microscopy, for which a fluorescently labeled polymer was used. Both techniques revealed details on the assembly of the protein-polymer conjugate at the oil-water interface.