Biomolecule Trapping With Stimuli-Responsive Polymer Coated Nanostructures

Abstract: Trapping biomolecules in nanosized gaps is of great interest in novel systems for single molecule analysis and membranes, which filter biomolecules. Current platforms are lacking in full functionality to facilitate biomolecule trapping and transport in their native environment and without covalent tethering to surfaces. Thus, we propose a system of thermo-responsive polymer poly(N-isopropylacrylamide) (PNIPAM) coated nanostructures, which are suited to controllably trap and release proteins, and overcome such challenges. PNIPAM polymer brushes (i.e. the barrier for proteins) on nanostructures were prepared via Activators Regenerated by Electron Transfer Atom Transfer Radical Polymerization (ARGET-ATRP) by employing a self-assembled monolayer of initiator molecules for the reaction. Variation of PNIPAM reaction time and/or solvent constituency during the polymerization results in different swollen/collapsed polymer brush thicknesses, indicated by the plasmonic shifts in extinction spectroscopy and surface plasmon resonance experiments. By having sufficient polymer film thickness and grafting density for nanowells, e.g. 120 nm, polymer conformational change below and above LCST allowed for controlled gating of these nanostructures. This feature was used to allow or block proteins from entering the interior of the nanostructures (small molecules diffuse freely in both states) as investigated by nanostructure plasmonic activity (extinction spectroscopy) and fluorescence microscopy below and above PNIPAM lower critical solution temperature (32 °C in water). In addition, with fluorescence microscopy experiments we showed that it is possible to trap and release many proteins with single nanowell resolution.