The invention relates to protein nanocapsules that exhibit material properties that change in different in vivo environments. A zwitterion moiety on the surface of the nanocapsule can protect the protein from opsonization in a first environment, yet uncouples from the protein nanocapsule in a second environment (e.g. at a pH of less than 6.5). In embodiments of the invention, the uncoupled protein nanocarrier is then internalized by mammalian cells (e.g. tumor cells).
