pH-Responsive and selective protein adsorption on an amino acid-based zwitterionic polymer surfaceElectronic supplementary information (ESI) available. See DOI: 10.1039/c5py00783f

The synergistic interactions between the α-amine and the carboxylic acid in an amino acid have recently been studied as bio-based zwitterions. Here, we report a new amphiphilic polymer containing glutamic acid grafted to the end of a dodecyl polymer side chain, which contains the α-amine and the γ-carboxylic acid of the glutamic acid moiety. The polymer self-assembled into a multilayered structure in the thin film, and the glutamic acid moieties in the polymer side chains were exposed to the polymer film/water interface. Annealing the sample enhanced the formation of a well-oriented lamellar structure in the films. Due to the presence of the glutamic acid moieties at the interface, the surface charge was controllable by pH in buffer solutions, resulting in zwitterionic character at neutral pH. It has been widely accepted that zwitterionic surfaces can exhibit non-fouling for proteins. Interestingly enough, the polymer film showed charge-selective protein adsorption since the synergistic interaction between the α-amine and the γ-carboxylic acid was weaker than conventional amino acid-based zwitterionic systems. This is due to the separated state of the functional groups by a three carbon spacer. An amphiphilic polymer bearing glutamic acid in the polymer side chain was used as a surface modifier to produce an amino acid-based zwitterionic surface with pH-responsive and selective protein properties.