Effect of Cellulose Nanofiber Length on Magnetic Separation Performance and Biotin–Streptavidin Conjugation Efficiency of CNF/Fe3O4 Composite Particles Prepared via Spray Synthesis

Abstract

Spray-dried TEMPO-oxidized cellulose nanofiber (TOCN)–Fe3O4 (TF) composite particles were fabricated using TOCNs of distinct fiber lengths, where the long TOCNs were approximately 3 times longer (around 1 μm) than the short TOCNs (approximately 350 nm). The objective was to elucidate how nanofiber aspect ratio governs particle morphology, magnetic performance, and bioaffinity. SEM and TEM analyses revealed that both TOCN types formed spherical particles (approximately 2–3 μm) with fibrous surface textures, yet the Fe3O4 distribution varied significantly. Short TOCNs promoted dense fiber entanglement within droplets, effectively entrapping Fe3O4 nanoparticles inside the particle core, whereas long TOCNs facilitated Fe3O4 migration toward the particle surface. Despite similar ζ-potentials (−44 to −49 mV) and superparamagnetic hysteresis behavior, surface Fe3O4 accessibility strongly influenced biofunctional response without altering magnetization. These findings provide a scalable strategy for designing bioactive magnetic cellulose composites with customizable surface reactivity for biosensing, biocatalysis, and magnetic separation in biomedical field.