Switchable interfaces with responsive polymer brushes for membrane protein assays

Surface modification by the in situ growth of polymer chains from surface-anchored initiators (the “grafting from” strategy) offers unique advantages in the design of switchable bio-interfaces with excellent mechanical stability. In combination with controlled polymerization techniques, in particular atom-transfer radical polymerization (ATRP), stimulus responsive polymer architectures with precise control over thickness, density and composition can be synthesized on a variety of substrates. These platforms are especially useful in biologically-oriented applications involving, for example, the confinement of membrane proteins onto solid supports for drug screening and biosensing purposes. Here surface functionalization strategies are often required to improve device biocompatibility and increase the mechanical stability of the bioassays over multiple sensing techniques and for several days. In our research activities, responsive polymeric interfaces based on pH-responsive poly(methacrylic acid) are grafted from micro/nanoporous platforms using surface-initiated ATRP to control ion permeation and thus selectively probe the functionality of supported membrane proteins. The reversible switching between swollen and collapsed conformations of the polymer brushes, as well as the ion gating properties of the chemically grafted nanopores, are characterized in situ by several surface-sensitive techniques. In parallel, tunable polymer layers are developed to guide the assembly of neutral lipid membranes with high mechanical stability and reproducibility on various synthetic materials. By controlling the polymer architecture using ATRP, we show that functional phospholipid membranes can be made to self-assemble on thin layers of charge-balanced poly(sulfobetaine methacrylate) from fusion of DOPC vesicles at physiological conditions. This study provides novel insight into the association states of grafted sulfobetaine-based polymers and how they relate to the surface hydration properties that have been largely exploited in the design of anti-biofouling interfaces. This research is part of the EU-FP7 program ASMENA “Functional Assays for Membrane Protein on Nanostructured Supports”.