Rapid Flow-Through Biocatalysis with High Surface Area, Enzyme-Loaded Carbon and Gold-Bearing Diatom Frustule Replicas

Hierarchically-porous, rigid inorganic structures have attracted appreciable interest in a wide range of applications, including catalysis, filtration, sensing, and energy storage/harvesting. Naturally-occurring, hierarchically-porous, rigid assemblies with a wide range of three-dimensional (3D) structures are generated by diatoms (photosynthetic aquatic microorganisms); that is, each of the tens of thousands of diatom species forms a macro-to-mesoporous, silica-bearing cell wall (frustule) with a particular, highly-reproducible 3D morphology. We have recently demonstrated that such intricate biosilica structures can be converted, without loss of 3D morphology, into high surface area (>1300 m2/g) macro-to-microporous carbon. Here we demonstrate, for the first time, how the chemical tailoring of such hierarchically-porous, carbon-converted, 3D biogenic structures can result in a high degree of enzyme loading for rapid flow-through catalysis. Two approaches have been developed for enriching such structures with carboxylic acid groups: i) dendritic amplification of partially-oxidized C replicas, and ii) electrochemical Au deposition followed by self-assembly of a carboxylic acid-bearing surface layer. The terminal carboxylic acid groups were then used for electrostatic attachment of a protamine (PA) modified derivative of the model enzyme, glucose oxidase (GOx-PA). In a flow-through system, the GOx-PA-loaded, diatom-derived microscale structures displayed a glucose consumption rate more than 80% faster than for GOx-PA-loaded C black and Au nanoparticles. The rapid flow-through catalysis of the carbon and gold-bearing frustule replicas was enabled by the open 3D morphology of the starting diatom silica templates, along with the enhanced surface area and high enzyme loading resulting from the chemical conversion and surface functionalization processes.