Date of Award

Spring 2021

Project Type

Dissertation

Program or Major

Chemical Engineering

Degree Name

Doctor of Philosophy

First Advisor

Jeffrey M Halpern

Second Advisor

Eva Rose M Balog

Third Advisor

Kyung Jae Jeong

Abstract

Elastin-Like-Polymers (ELPs) are intrinsically disordered biopolymers with an amino acid structure comprised of the pentapeptide repeat sequence [VPGXG]n (V = valine, P = proline, G = glycine, X = guest residue, and n = total number of repeat sequences). ELPs are stimuli-responsive meaning below their transition temperature, ELPs are structurally disordered, highly solvated, and soluble in aqueous solutions. Above their transition temperature, ELPs experience coalescence and phase separation as intermolecular and intramolecular contacts form within the hydrophobic regions of the ELPs. The transition temperature of ELPs is influenced by the hydrophobic surface area, as well as changing solvent conditions including pH or ionic strength, creating ELPs with unique stimuli-response profiles. The stimuli-response of surface-immobilized ELPs was previously modeled as extension and collapse; in the extended state, the ELPs are more solvated. The collapsed state is characterized by increased intermolecular and intramolecular contacts within the hydrophobic regions of ELPs, triggered by changing environment stimuli. Therefore, we sought to use electrochemistry to validate the proposed stimuli-response model of surface-immobilized ELP in the development of a stimuli-responsive biosensor for the point-of-care detection and quantification of interleukin-6 (IL-6). The proposed biosensor design is comprised of streptavidin-ELP bioconjugate immobilized on the biosensor surface used to capture biotinylated antibodies to bind IL-6. We hypothesized IL-6 binding will alter the hydrophobic surface area of the ELP-streptavidin bioconjugate influencing the transition temperatures and stimuli-responsive properties based on the extent of IL-6 bound. In the development of a stimuli-responsive biosensor, a reproducible surface-immobilization protocol for ELPs was first optimized immobilizing ELPs on gold using thiol-chemistry. The stimuli-response of surface-immobilized I40 was characterized, exposing the ELP modified electrodes to varying molarities of sodium chloride. The stimuli-response model of surface-immobilized ELPs as extended and collapsed was validated using electrochemistry. Including additional characterization of stimuli-response reversibility and inclusion of intermediate values was observed between the maximum and minimum response indicating surface-immobilized ELPs undergo transient states between extension and collapse. Further progress on the development of a stimuli-responsive ELP biosensor was achieved by the bioconjugation of streptavidin to surface-immobilized ELPs. Preliminary data supports the current carbodiimide bioconjugation approach of hydrazide functionalized streptavidin to surface-immobilized ELPs, however, stability of the modified electrode surface and inconsistencies in the impedance response prevent full validation, suggesting further characterization and optimization is required.

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