Polymer Brushes for Bioanalytical Applications

Licentiatavhandling, 2025

When polymers are grafted from a surface at a high surface coverage, and exposed to a liquid environment, it promotes stretching of the chains up and perpendicular to the surface, forming a "brush" structure. These nanoscale “polymer brushes” are commonly used as surface coatings for their protein repelling (antifouling) properties, where the polymer brushes prevent proteins and larger molecules from attaching to the surface. However, polymer brushes can also add functionality to the surface by using stimuli-responsive monomers in the polymerisation.

In this work, three bioanalytical applications of functional polymer brushes have been investigated. Thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) was used for long-term stable trapping of enzymes in nanoscale chambers (one attoliter large). Once trapped in the chambers, the enzymes were demonstrated to retain their activity and were successfully used in enzymatic reactions, including the conversion of lactose to d-glucono-1,5-lactone and cycling of the cofactor nicotinamide (NADH) and its oxidised equivalent (NAD+). pH-responsive poly(acrylic acid) (PAA) was used for covalent immobilisation of enzymes for biosensing purposes. The immobilised enzymes were demonstrated to react with non-electrochemically active analytes and generate an active product, allowing electrochemical detection of the analyte. This, coupled with the antifouling properties of the brush, allowed for detection of the non-electrochemically active neurotransmitters glutamate and acetylcholine, even in diluted cerebrospinal fluid (CSF), a complex biofluid. Finally, poly(N-hydroxyethylacrylamide) (PHEAA) was investigated as a selective diffusion barrier for macromolecular transport of poly(methacrylic acid) shuttles, mimicking the selective transport of the nuclear pore complex (NPC).