Protein immobilization using complex coacervates and complex coacervate thin films

Abstract

Enzymes can enable a wide and growing range of chemistries, often outperforming synthetic catalysts. However, enzymes must often be converted to heterogeneous catalysts. Protein immobilization enables this conversion and can enhance the stability of enzymes. Complex coacervates are highly effective at encapsulating and stabilizing enzymes. This thesis demonstrates the use of complex coacervate thin films for the immobilization of enzymes and systematically probes methods to enhance the performance of these materials. The first study presents a proof-of-concept demonstration of complex coacervate thin films for the synthesis of functional biomaterials. The immobilization method itself is all-aqueous, reducing the likelihood of enzyme denaturation, and facile, only requiring two steps: coating followed by crosslinking.

A model biosensor was synthesized and demonstrated to have both high sensitivity and selectivity, and the immobilization method imparted increased thermal stability on the enzyme. From here, two directions were explored: how protein properties affect their coacervation behavior and optimizing the performance of the complex coacervate thin films. The second study aims to quantify the surface charge distribution or the "patchiness" of proteins and relate this to their complexation behavior. A patchiness parameter that averaged pair correlations between neighboring points on the protein surface was shown to correlate with the coacervation behavior of proteins with greater patchiness favoring the formation of complexes. Further work will enable this parameter to be incorporated with other protein properties in order to create robust predictive algorithms for protein-polymer coacervation.

The third and fourth studies aimed to enhance the performance and properties of complex coacervate thin films. The third study probed whether the morphology of these composite materials could be controlled and found that morphologies varied greatly as a function of the polyelectrolyte strength and the loading of the encapsulated molecule. The strongest interactions led to precipitation, but weaker interactions led to micellization in both solution and the films. The fourth study aimed to understand how various polymer properties, including polyelectrolyte strength and monomer conformational freedom, affect the performance of complex coacervate thin films. Strong interactions were found to favor greater catalytic activity but lower stability, while weaker interactions favored greater stability.