Rhodamine B‐Modified Nanocrystalline Cellulose as Fluorescent Sensor for Fe³⁺ Ion Detection

Abstract Iron is crucial for various biological processes in humans, animals, and plants, making precise and efficient monitoring of iron ion concentrations essential. To address this need, a cellulose‐based smart fluorescent material (NCC@NH 2 @RB) with a conjugated structure is designed and synthesized for the rapid and sensitive detection of Fe 3+ ions. This sensor features core‐shell nanoparticles functionalized with rhodamine B (RB), using (3‐aminopropyl)triethoxysilane (APTES) as a linker. The resulting fluorescent probe, composed of nanocrystalline cellulose and RB, exhibits strong fluorescence under ultraviolet light, making it an effective tool for Fe 3+ ion detection in water. When Fe 3+ ions are introduced into a solution containing NCC@NH 2 @RB, they bind with weak‐field ligands such as nitrogen and oxygen in the probe's structure, forming complexes. This interaction involves high‐spin coordination and leads to the self‐assembly of Fe 3+ ions on the surface of NCC@NH 2 @RB. The process generates single electrons, increasing paramagnetism and quenching the fluorescence. The NCC@NH 2 @RB fluorescent probe has a limit of detection (LOD) of 0.01 µM and a limit of quantification (LOQ) of 0.03 µM with linearity at concentrations of 1.0 × 10 −4– 2.5 × 10 −3 m . This fluorescence quenching effect is specific to Fe 3+ ions, ensuring that the probe remains unaffected by other metal ions.