Examining Ferrihydrite Nanomaterials: From Structure and Biosynthesis to Biomedical and Agricultural Applications

This multidisciplinary work is an attempt to synthesize advances in ferrihydrite (Fh, Fe10O14(OH)2·nH2O) research and applications ranging from physics to nanoagriculture. Fh nanoforms obtained via chemical or “green” synthesis methods using various bacterial cultures display unique catalytic and enzyme-like properties, surface reactivity, and magnetic properties. SAXS and SANS, supported by model-dependent fitting (FITTER) and model-independent ATSAS tools (Guinier approximation, p(r) function, and ab initio reconstruction), together with Porod-law and fractal analysis, provide a coherent multi-scale picture. Biogenic nanoparticles produced by Klebsiella oxytoca are built from 1–2 nm crystallites embedded in an organic matrix and exhibit a cultivation-dependent, hierarchical architecture: e.g., Fe12 yields a two-level hierarchical structure, whereas Fe34 produces a sponge-like surface. SANS further reveals that ferrihydrite nanoparticles in complex with lactate dehydrogenase form a core–shell bionanocomposite. The practical applications lie primarily in the biomedical field and plant cultivation, with significant implications for medicine and food production. A more thorough understanding of the underlying mechanisms, as well as studies to determine precise dosages and application methods, is critical. Investigating the biological activity of Fh NPs under both physiological and pathological conditions will facilitate the development of biologically informed engineering strategies for new Fh-based agents aimed at treating serious human diseases, improving plant mineral nutrition, protecting plants from phytopathogens, and remediating soil. Future directions include engineering nano-agrochemicals by functionalizing nanoforms tailored to specific crop types and soils with distinct physicochemical properties.