Protein crystals as nanotemplating materials
Date
2019
Authors
Kowalski, Ann, author
Snow, Christopher, advisor
Kipper, Matt, committee member
Peebles, Christie, committee member
Sambur, Justin, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
The advancement of nanomaterial development depends on the reliable and scalable synthesis of three dimensional nanostructures and devices. Applications for these materials range from catalysis and energy storage to biomedicine and imaging. Towards the goals of shape-controlled immobilization and synthesis, templating is arising as a promising manufacturing method. With the rise of bionanotechnology, DNA and protein scaffolds can be designed, synthesized, and functionalized to coordinate nanoparticles, enzymes, and other guests in three dimensions, or act as molds for the synthesis of anisotropic nanostructures. Inherently, protein crystals are an attractive target, as they have nearly unlimited designability, intrinsic functionality for a variety of useful materials, and mild reaction conditions. The overarching goal of this work is to explore the feasibility of protein crystals as templates for the creation of biohybrid materials. We show that protein crystals with large solvent channels can strongly adsorb and immobilize gold nanoparticles by reversible metal affinity interactions and that these nanoparticles can serve as nucleation sites for the growth of nanorods within the pores of protein crystals by a variety of gold growth methods. We show that, depending on the method used, gold nanorod synthesis within the crystals can be dependent on the presence of a seed particle. Despite their stability, these crystals can be dissolved to release the gold structures, which can be analyzed by electron microscopy and elemental analysis. A variety of gold nanorod products are formed, from highly anisotropic individual rods, to interconnected rod bundles, to parallel rods embedded within a protein matrix. Additionally, we show that protein crystal pores can be used for the long-term capture of multiple enzymes and that these enzymes retain their activity within the crystal. Product can be separated by a simple washing step, and the immobilized two-enzyme pathway can be used for multiple cycles over several weeks. Rates of product formation are higher for enzymes immobilized within crystals of a high surface-to-volume ratio; thus, the use of micron-sized crystals minimizes transport limitations typically associated with enzyme immobilization. Preliminary work suggests the crystals may also impart significant thermal stability to the embedded enzymes. Porous protein crystals may provide a superior templating method for the development of nanomaterials. Here we further demonstrate the wide variety of applications for protein crystals by revealing their success as scaffolds for immobilization, synthesis, and catalysis.