Reproducibly Modified Elastin-like Polymer Gold Electrode Surfaces

Elastin-like polymers (ELPs) have been used for a variety of biomedical applications, including drug delivery and tissue scaffolding. ELPs are useful due to their adjustable lower critical solution temperature and tunable structure for different applications. However, despite ample characterization of ELPs in aqueous solutions, the characterization of ELPs on surfaces is less well explored. For example, sources of inconsistency in ELP modification to surfaces have yet to be explored in detail. Surface modifications of large macromolecules often suffer from poor reproducibility and inconsistent measurements. We developed and optimized a method for modifying a gold electrode surface with ELPs using a thiol-gold interaction through a single cysteine residue near the N-terminus. The modification parameters were tuned for reproducible charge-transfer resistance of the surface, as measured by electrochemical impedance spectroscopy. The final optimized surface modification parameters, without dimethyl sulfoxide or other cosurfactant treatment, are 0.0125 mg/mL ELP for 30 min at 4 °C in 3.5 mM TCEP in ultrahigh-purity water at pH 7.4. The relative amount of cysteine modified to gold versus ELP solution concentration was determined via thiol reduction. Using these data, the source of poor reproducibility was confirmed to be nonspecific polymer interactions.