Biomolecule Functionalization of Poly(3,4-ethylenedioxythiophene) Surfaces via Thiol-Maleimide Click-Chemistry

Modifying the surface chemistry of poly-(3,4-ethylenedioxythiophene) (PEDOT) with biological moieties is of interest for optimizing interactions in biointerfacing applications. Here, we demonstrate the attachment of cholesterol, a lipid prevalent in animal blood and cell membranes, and cysteine, an amino acid prevalent in proteins, onto PEDOT surfaces through efficient thiol-maleimide click-chemistry between maleimide-functionalized PEDOT (PEDOT-MA) and corresponding thiol derivatives. The reaction process of cholesterol post-treatment was actively monitored by electrochemical impedance spectroscopy (EIS) taken at different incubation times. An equivalent circuit model was used to deconvolute the impedance data. It was found that the charge transfer capability, as well as the ion diffusion within the PEDOT film, decreased systematically with incubation time. However, the film resistance remained unchanged in this process, indicating the relatively unaffected bulk properties. This finding was supported by scanning electron microscopy (SEM) results where no significant morphological changes were observed after the post-treatment. In addition, the charge storage capability also decreased, with only 23% of the original capacitance remaining after the post-treatment. The water contact angle increased from 23 to 115° after the cholesterol binding, confirming the formation of a hydrophobic film that correlates with the decreased charge transport behavior. In contrast, the attachment of cysteine showed almost no effect on the charge transport behavior and charge storage capability of PEDOT-MA. Contact angle measurements confirmed the high hydrophilicity of the cysteine-treated film. Again, SEM experiments showed there were no significant changes in the surface morphology. X-ray photoelectron spectroscopy (XPS) confirmed the presence of cholesterol and cysteine on the sample surface. Our results demonstrate that thiol-maleimide click-chemistry provides an efficient and effective route for the surface functionalization of PEDOT with biomolecules.