Phase transition polymers swell or collapse in aqueous media as a response to external stimuli. This transition can be triggered by a change in temperature, pH, ionic strength or even by a binding event based on biochemical recognition. The latter makes them attractive candidates for switchable elements of biosensors. The goal of this work is to develop a readout system for biomolecular interactions based on the structural changes within a polymer triggered by a specific binding event and an enzymatic reaction as signal amplification.

For this purpose, two architectures for surface modification are investigated. Both are built in two steps: First, a layer-by-layer (LBL) assembly is prepared on the surface of a gold electrode. In a second step, a terminal layer containing a polymerization initiator is used to grow a LCST (Lower Critical Solution temperature) polymer from the surface. Enzyme immobilization takes place either in the LBL assembly (fig. 1a) or in the LCST-polymer matrix (fig. 1b). The assembly steps are monitored by Quartz Crystal Microbalance with Dissipation (QCMD). The switching behavior of these modified electrodes is then assessed by measuring the charge transfer resistance and transformation of a redox mediator for the enzymatic reaction as a function of temperature. The catalytic efficiency of the enzyme is determined by (spectro)electrochemical methods.

We report on the synthesis and characterization of these modified surfaces. These preliminary results demonstrate the possibility of immobilizing the enzymes underneath or inside the switchable polymer cover. In further steps, the switchable polymer brush will be furnished with virus recognition sites to implement the biosensing functionality.

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1. Enhancing heterogeneous electron transfer between enzymes and electrodes
2. Gold Nanoparticles as Support for the Direct Electron Transfer and Catalysis of the Human Sulfite Oxidase
3. Electrochemical observation of the thermally induced phase transition for a switchable polymer immobilised onto gold electrodes