Biomolecule Trapping With Stimuli-Responsive Polymer Coated Nanostructures
Doctoral thesis, 2022

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.

biomolecule transportation

protein interaction

polymer brushes

quartz crystal microbalance with dissipation monitoring

fluorescence microscopy


surface plasmon resonance

poly(ethylene glycol)

KE, Chemistry and Chemical Engineering Department, Chalmers University of Technology
Opponent: Prof. Tapani Viitala, University of Helsinki, Finland


Justas Svirelis

Chalmers, Chemistry and Chemical Engineering, Applied Chemistry

Detecting and analyzing single or a few biomolecules such as proteins is crucial to develop novel drugs and understand disease formation. In human organisms alone, at least around 20 000 different proteins exist. However, only around a quarter of these have been studied for their function, behavior in different environments and structural change over time. Mostly until now, biomolecules have been investigated in bulk. This means that if a smaller fraction of the same protein sample behaves differently over time, it will not be detected as the majority of the other proteins will “mask” their detection. Nowadays, an increasing number of tools allow to study single or a few proteins, which could present a clearer understanding of how the whole sample might behave. Nevertheless, the analyses are usually limited as the protein’s freedom is often restricted in some way, the molecules move out of the focal point before they can be observed, or the experimental environment does not mimic the native picture in full.
To tackle some of the mentioned challenges, we envisioned a system, which would allow proteins to freely roam around at physiological conditions while confining them in the detection spot. Such a volume should be relatively tiny as an average protein’s diameter ranges between 3 and 6 nanometers. Therefore, a platform containing some sort of a nanocavity with a tunable gating mechanism could deem advantageous in achieving this.
Nanosized objects are often difficult for people to relate to as they are incredibly small. An example of such scale could be by roughly comparing the diameters of a common football ball and the Sun.
In this thesis, a novel platform to trap and release biomolecules on demand was designed and its working principle is shown. The platform is made of out multiple or a few nanostructures (or nanowells), which are the supports for the confinement of proteins. Furthermore, they are coated with temperature-responsive polymer brushes, which act as a smart-gate and do not damage or restrict these biomolecules in any way. Finally, trapping and analyzing proteins in many nanocavities in parallel at the same time could possibly allow to increase the throughput of coming investigations manyfold.
All in all, we highly hope that our manufactured system combined with other methods will help other researchers and medical facilities to better understand how various proteins (other biomolecules as well) function, change their shape over time and interact with others in the future.

SIMONANO (Single Molecule Analysis in Nanoscale Reaction)

Familjen Erling-Perssons stiftelse (SIMONANOStartingGrantADahlin), 2018-02-01 -- 2019-12-31.

Single Molecule Analysis in Nanoscale ReactionChambers SIMONANO2

European Commission (EC) (EC/H2020/101001854), 2021-02-01 -- 2026-01-31.

Subject Categories

Polymer Chemistry

Physical Chemistry

Biochemistry and Molecular Biology

Materials Chemistry


Nano Technology

Medical Materials


Chalmers Materials Analysis Laboratory

Nanofabrication Laboratory



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5205



KE, Chemistry and Chemical Engineering Department, Chalmers University of Technology

Opponent: Prof. Tapani Viitala, University of Helsinki, Finland

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