Protein-selective adsorbers by molecular imprinting via a novel two-step surface grafting method

Molecularly imprinted polymers (MIP) offer in principle a robust, cost-efficient alternative to antibodies, but it is still a challenge to develop such materials for protein recognition. Here, we report the molecular imprinting of a functional polymeric hydrogel layer with lysozyme as the template in a two-step grafting procedure by a novel initiation approach on track-etched polyethylene terephthalate membrane surface. This is based on surface functionalization with aliphatic C-Br groups which can be used as an initiator for surface-initiated atom transfer radical polymerization (SI-ATRP) and photo-initiated copolymerization. At first, the scaffold poly(methacrylic acid) (PMAA) was obtained through SI-ATRP of poly(tert-butyl methacrylate) and subsequent hydrolysis. Thereafter, it was assembled with the template to form a stable PMAA/lysozyme complex. In the second step, a polyacrylamide (PAAm) hydrogel was synthesized via UV-initiated surface grafting/crosslinking copolymerization around the scaffold/protein complex. Finally, the template was eluted to yield the grafted hydrogel layer with binding sites having complementary size, shape and appropriate arrangement of the functional groups to rebind lysozyme. The selectivity of lysozyme recognition, relative to cytochrome C with a similar size and isoelectric point, was increased by optimization of the scaffold chain length, UV grafting/crosslinking time and the chemical crosslinking degree of the PAAm-based hydrogel. The feasibility for the development of protein MIP in a straightforward way by independent optimization of crucial parameters - structures of scaffold with functional groups and of the crosslinked hydrogel matrix - have been demonstrated.