AbstractHierarchicallyâporous, rigid inorganic structures have attracted appreciable interest in a wide range of applications, including catalysis, filtration, sensing, and energy storage/harvesting. Naturallyâoccurring, hierarchicallyâporous, rigid assemblies with a wide range of threeâdimensional (3D) structures are generated by diatoms (photosynthetic aquatic microorganisms); that is, each of the tens of thousands of diatom species forms a macroâtoâmesoporous, silicaâbearing cell wall (frustule) with a particular, highlyâreproducible 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) macroâtoâmicroporous carbon. Here we demonstrate, for the first time, how the chemical tailoring of such hierarchicallyâporous, carbonâconverted, 3D biogenic structures can result in a high degree of enzyme loading for rapid flowâthrough catalysis. Two approaches have been developed for enriching such structures with carboxylic acid groups: i) dendritic amplification of partiallyâoxidized C replicas, and ii) electrochemical Au deposition followed by selfâassembly of a carboxylic acidâbearing 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 (GOxâPA). In a flowâthrough system, the GOxâPAâloaded, diatomâderived microscale structures displayed a glucose consumption rate more than 80% faster than for GOxâPAâloaded C black and Au nanoparticles. The rapid flowâthrough catalysis of the carbon and goldâbearing 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.