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@NH₂@RB) with a conjugated structure is designed and synthesized for the rapid and sensitive detection of Fe³⁺ 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 Fe³⁺ ion detection in water. When Fe³⁺ ions are introduced into a solution containing NCC@NH₂@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 Fe³⁺ ions on the surface of NCC@NH₂@RB. The process generates single electrons, increasing paramagnetism and quenching the fluorescence. The NCC@NH₂@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 Fe³⁺ ions, ensuring that the probe remains unaffected by other metal ions.