Next‐Generation Polymer Shells for Inorganic Nanoparticles are Highly Compact,Ultra‐Dense,and Long‐Lasting Cyclic Brushes

Cyclic poly‐2‐ethyl‐2‐oxazoline (PEOXA) ligands for superparamagnetic Fe₃O₄ nanoparticles (NPs) generate ultra‐dense and highly compact shells, providing enhanced colloidal stability and bio‐inertness in physiological media. When linear brush shells fail in providing colloidal stabilization to NPs, the cyclic ones assure long lasting dispersions. While the thermally induced dehydration of linear PEOXA shells cause irreversible aggregation of the NPs, the collapse and subsequent rehydration of similarly grafted cyclic brushes allow the full recovery of individually dispersed NPs. Although linear ligands are densely grafted onto Fe₃O₄ cores, a small plasma protein such as bovine serum albumin (BSA) still physisorbs within their shells. In contrast, the impenetrable entropic shield provided by cyclic brushes efficiently prevents nonspecific interaction with proteins.