Biopolymers for biosensors: polypeptide nanotubes for optical biosensing

In this work, N-carboxy anhydride (NCA) monomer molecules were condensed on the pore walls of an initiator-coated nanoporous alumina template, leading to polypeptide (poly(gamma-benzyl-L-glutamate), PBLG) film formation. Three different ways were followed for peptide nanotube formation: NCA polymerization in solution, in melt and polymerization from surface-nitiated vapor deposition. While the NCA monomer was polymerized within the pores, the wall thickness of the resulting polypeptide was tuned by changing the polymerization time. This polypeptide-coated alumina membrane will be used as planar optical waveguide to monitor both the changes in the refractive index and fluorescent signals of the composite membrane through specific binding of a bioanalyte. We monitored for the first time the in-situ formation of an initiator layer (3-Aminopropyltriethoxysilane, APTE) inside the pores of an alumina membrane via optical waveguide spectroscopy. Attachment of initiator molecule effectively changed the dielectric constants of the interfaces, resulting in detectable shifts of the waveguide modes. We have previously demonstrated that unmodified nanoporous alumina waveguide sensor having a 10 times higher sensitivity than surface plasmon spectroscopy (SPR). The sensitivity may be further increased if the pores are coated with PBLG polypeptides, which has many functional sites on each polypeptide chain.