Elastin-like polymers (ELPs) are intrinsically disordered biopolymers with a dynamic structure comprised of the repetitive amino acid sequence [VPGXG]n (V = valine, P = proline, G = glycine, X = guest residue, and n = total number of repeats). ELPs adopt environment dependent conformations and interactions resulting in what is described as their stimuli-response. Below their transition temperature, ELPs are soluble with decreased intermolecular interactions. Above their transition temperature, ELPs promote intra- and intermolecular interactions within their hydrophobic regions to minimize unfavorable interactions with the aqueous environment.
A previously proposed model of the stimuli-response of surface-immobilized ELPs describes the response as extension and collapse. The collapsed state describes ELPs above their transition temperature where non-polar intermolecular and intra-molecular contacts between and within ELP are favored resulting in quantifiable morphological changes. To promote point-of-care use for biosensor technology, we sought to use electrochemistry to validate the stimuli-response model of extension and collapse for surface-immobilized ELPs.
Electrochemical impedance spectroscopy (EIS) was used to measure impedance, the total opposition to current flow at the electrode/electrolyte interface comprised of various resistive processes. Charge transfer resistance, a component of impedance, is increased by the formation of an insulating layer on the electrode surface decreasing the available electrode surface area for electron transfer. Within this work, EIS was used to demonstrate reproducibility of the surface-immobilization of ELPs. Including subsequent characterization of the stimuli-response of surface-immobilized ELPs, demonstrating the response to be reversible and inclusive of intermediate states between extension and collapse of ELPs.
