Switching behavior of biomolecules attached to a responsive polymer brush
N Akkilic, J C Prangsma, F A M Leermakers, C Blum and W M de Vos
University of Twente, The Netherlands Wageningen University, The Netherlands
: J Electr Eng Electron Technol
Abstract
Many investigations over the years have shown that the interaction of surface grafted polymer brushes with biomolecules, e.g. proteins, receptors, has a great importance for a significant number of applications. Here we present on the design of a smart polymer brush/biomolecule architectures, produced via the “grafting to†approach. For this, individual protein molecules, labelled with the fluorophore ATTO488, were covalently attached to a single, pH responsive poly(acrylic acid) (PAA) brush. Subsequently, total internal fluorescence microscopy (TIRF) was used to monitor intensity changes over time, when switching between low and high pH. We show that the fluorescence intensity of a single protein molecule shows an on-off switching behavior, controlled by the solution pH. Fluorescence intensity is quenched (off state) by 85% when the PAA chains are stretched at basic pH, yet we observe an enhancement in the fluorescence (on state) when the polymer chains collapse at basic pH. Furthermore, we use the local density of optical states (LDOS) effect to predict the location of a molecule that is covalently (or electrostatically) attached to a polymer brush. Fluorescence lifetime was 3.5 ns when the polymer was stretched away from the grafting interface at basic pH, whereas the lifetime is quenched to just 2 ns at acidic pH. Moreover, we support our experimental results with numerical self-consistent field (nSCF) theory. Biomolecules can be either in (on state) or outside (off state) of the brush and by fine-tuning the brush parameters and particle size it becomes possible to use this system as a biosensor.
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