Poly(N-Isopropylacrylamide) Polymer Brush Functionalized Nanostructures as Thermo-Responsive Gating Systems for Protein Transportation

Licentiate thesis, 2021

Controlling molecule translocation through nanosized gaps is of great interest in novel systems for single molecule analysis and biomolecular membranes. The molecular gating property of thermo-responsive end-grafted poly(N-isopropylacrylamide) (PNIPAM) polymer brushes on well-shaped gold-silica nanostructures is intended to be investigated for controlled protein transportation via extinction spectroscopy and fluorescence microscopy methods below and above PNIPAM lower critical solution temperature (LCST; 32 °C in water). Polymer brushes are prepared via Activators Regenerated by Electron Transfer Atom Transfer Radical Polymerization (ARGET-ATRP) by employing Bis[2-(2- bromoisobutyryloxy)undecyl] disulfide (DTBU) and its thiol (TBU) equivalent as initiators for the reaction. Variation of PNIPAMreaction time/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 thickness and grafting density for, e.g. 80-90 nm, nanowells, polymer conformational change below and above LCST, allows controlled gating of these nanostructures. This feature was employed for protein transportation through the polymer brush interface in and out of the fabricated nanowell according to its plasmonic activity. In addition, we investigated molecular gating of fluorescently labelled protein transportation by complimentary fluorescence microscopy measurements.