Solid-phase PEGylation of an immobilized protein cage on polyelectrolyte multilayer

We used a quartz crystal microbalance (QCM) to quantitatively characterize solid-phase poly(ethylene glycol) modification (PEGylation) of apoferritin that was electrostatically immobilized on the surface of a polyelectrolyte multilayer. The solid-phase PEGylation processes were monitored by analyzing QCM frequency shifts, which showed that the PEG chains were covalently introduced onto the surface of the immobilized apoferritin. We investigated the effect of PEG concentration, PEG molecular weight, and two-dimensional coverage of the immobilized apoferritin on the solid-phase PEGylation process in addition to the surface properties of the PEGylated apoferritin film, such as wettability and protein adsorption capacity. Since the reaction field is more spatially restricted in solid-phase PEGylation than in traditional aqueous-phase PEGylation, this study shows that a ferritin protein cage is potentially useful as a tailored building block, one that has well-defined structures different from the PEGylated ferritin prepared by an aqueous-phase approach.