Nature has perfected the art of nanofabrication through intricate biomineralized structures such as diatom frustules and coccolithophores. These microorganisms produce highly ordered, porous architectures composed of silica (in diatoms) or calcium carbonate (in coccolithophores), exhibiting exceptional mechanical strength, optical properties, and hierarchical porosity. Their precisely controlled morphologies make them ideal templates for synthesizing advanced nanomaterials via sol-gel chemistry or atomic layer deposition (ALD). By leveraging these biological scaffolds, researchers can replicate their nanostructures to create functional materials for photonics, catalysis, and biosensing, while also confronting challenges in scalability and morphology control.

Diatom frustules consist of nanoporous silica with periodic arrangements of pores, ridges, and chambers, often exhibiting photonic crystal-like behavior. Coccolithophores, on the other hand, produce calcium carbonate plates with intricate sub-micrometer features. Both structures are formed under mild physiological conditions, offering an eco-friendly alternative to synthetic nanofabrication. To replicate these architectures, sol-gel methods are commonly employed for silica-based frustules, while ALD is used to deposit conformal coatings or convert biogenic templates into new materials.

In sol-gel replication, diatom silica serves as a sacrificial template. The process involves infiltrating the frustule pores with a precursor solution, such as titanium isopropoxide for TiO2 or tetraethyl orthosilicate for SiO2, followed by gelation and calcination to remove the organic template. The resulting replica retains the diatom’s original morphology but with altered composition, enabling tailored optical and catalytic properties. For coccolithophores, ALD can deposit thin films of oxides or metals onto the calcium carbonate scaffold, preserving the intricate features while imparting new functionality. Sequential exposure to gaseous precursors, such as trimethylaluminum and water for Al2O3, ensures uniform coating even in high-aspect-ratio nanostructures.

The replicated materials exhibit unique photonic properties due to their inherited periodic nanostructures. Diatom-derived silica replicas have been demonstrated to enhance light harvesting in photonic devices, with pore arrangements acting as natural diffraction gratings. When converted into TiO2 or ZnO, these structures show improved photocatalytic activity due to their high surface area and light-trapping capabilities. Coccolithophore-templated materials, when coated with plasmonic metals like gold or silver, exhibit enhanced Raman scattering for surface-enhanced spectroscopy applications. The hierarchical porosity of these replicas also facilitates efficient mass transport, making them suitable for catalytic reactors or sensor platforms.

In catalysis, diatom-templated materials provide a high surface area and well-defined pore networks that enhance reactant diffusion and active site accessibility. For instance, Ni-doped diatom silica replicas have been used for methane dry reforming, achieving higher conversion rates compared to conventional catalysts. Similarly, coccolithophore-derived structures coated with Pt or Pd nanoparticles demonstrate improved selectivity in hydrogenation reactions. The nanoscale curvature and porosity of these templates influence metal nanoparticle dispersion, preventing aggregation and maintaining catalytic activity.

Biosensing applications benefit from the biocompatibility and optical properties of these biogenic templates. Diatom replicas functionalized with antibodies or DNA probes can serve as label-free sensors, where the photonic crystal effect amplifies signal transduction. The large surface area allows for high probe density, improving detection limits for biomarkers. Coccolithophore-based sensors, when coated with fluorescent dyes or quantum dots, enable multiplexed detection due to their distinct optical signatures. The ability to tailor surface chemistry further enhances selectivity for target analytes in complex biological matrices.

Despite these advantages, challenges remain in scaling up production and achieving precise morphology control. Diatom cultivation requires optimized conditions to ensure uniform frustule morphology, as variations in nutrient availability or temperature can alter pore size and arrangement. Harvesting and purification of diatoms or coccolithophores must be cost-effective to compete with synthetic templates. Additionally, sol-gel and ALD processes must be carefully tuned to avoid pore clogging or incomplete infiltration, which can compromise replica fidelity. For ALD, precursor diffusion limitations in high-aspect-ratio structures may lead to non-uniform coatings.

Morphology control is particularly critical for photonic applications, where slight deviations in periodicity can drastically alter optical properties. Researchers have explored genetic engineering of diatoms to tailor frustule patterns or chemical modification of coccolithophores to stabilize their structures during replication. Advances in computational modeling help predict optimal template geometries for specific applications, guiding the selection of biological scaffolds. However, achieving consistent replication across large batches remains a hurdle for industrial adoption.

The environmental sustainability of using biogenic templates is a notable advantage over conventional nanofabrication, which often involves toxic chemicals or energy-intensive processes. Diatoms and coccolithophores grow in aqueous environments at ambient temperatures, minimizing the carbon footprint of template production. Furthermore, the ability to convert these templates into functional materials without harsh etching steps aligns with green chemistry principles. Future developments may focus on enhancing the mechanical stability of replicas for demanding applications or integrating them into hybrid devices combining multiple functionalities.

In summary, diatom frustules and coccolithophores offer a versatile platform for nanomaterial synthesis, bridging the gap between biological precision and engineered functionality. Their intricate architectures enable the fabrication of replicas with applications spanning photonics, catalysis, and biosensing. While scalability and morphology control present ongoing challenges, advances in biotemplating techniques and process optimization continue to expand their potential. By harnessing these natural nanostructures, researchers can develop sustainable, high-performance materials with tailored properties for next-generation technologies.