Cellulose-Based Sensor Containing Phenanthroline for the Highly Selective and Rapid Detection of Fe Ions with Naked Eye and Fluorescent Dual Modes.

Iron ions play a vital role in many biological processes, and their concentrations are responsible for human health. Therefore, it is essential to detect the concentration of iron ions by a rapid, accurate, highly selective, and practical method. Herein, we have synthesized a cellulose-based fluorescent sensor (Phen-MDI-CA) for the highly selective and rapid detection of Fe ions via chemically bonding 1,10-phenanthroline-5-amine (Phen) onto cellulose acetate (CA) using 4,4'-methylene diphenyl diisocyanate (MDI) as a cross-linker. Benefiting from the anchoring and diluting effect of a cellulose skeleton, the resultant Phen-MDI-CA displays excellent fluorescence properties in both solution and solid state. More interestingly, a cellulose-based polymer chain significantly improves the sensitivity of phenanthroline to Fe ions. Upon meeting Fe ions, a red, insoluble, and nonfluorescent Fe-(Phen-MDI-CA) complex appears immediately; thus, Phen-MDI-CA can work as a multimode chromogenic sensor for the highly selective, sensitive, and rapid detection of Fe ions. In the instrument-free visual mode, the detection limit for Fe ions is 50 ppb, and in fluorescence mode, the detection limit is 2.6 ppb. To our knowledge, this is the first time that such a low detection limit for Fe ions in aqueous media has been observed by the naked eye. In addition, Phen-MDI-CA has good solubility and processability in common organic solvents, which facilitates its use in different material forms, e.g., printing ink, coating, and film. Therefore, the Fe-responsive and chromogenic Phen-MDI-CA exhibits a huge potential in the detection and extraction of Fe ions.