Ferric ion detection mechanism of a dicarboxylic cellulose nanocrystal and a 7-amino-4-methylcoumarin based fluorescent chemosensor.

As one of Earth's most widely distributed and abundant elements, iron impacts the natural environment and biological systems. Therefore, developing a simple, rapid, and accurate Fe detection method is vital. Fluorescent dicarboxylic cellulose nanocrystals (FDCN) with selective quenching of Fe were synthesized using 7-amino-4-methylcoumarin (AMC), and dicarboxylic cellulose nanocrystals (DCN) prepared by sequential periodate-chlorite oxidation. The sensing characteristics and detection mechanism of FDCN for Fe were studied by fluorescence spectrophotometry, Fourier-transform infrared spectroscopy (FTIR), the Stern-Volmer equation, Job's plot method, and the Benesi-Hildebrand equation. The results showed that FDCN was highly selective for Fe, and other metal ions did not reduce the selectivity. High sensitivity with a detection limit of 0.26 μM and a Stern-Volmer quenching constant of 0.1229 were also achieved. The coordination between Fe and the carboxylic, hydroxyl, and amide groups on the surface of FDCN and the carbonyl of coumarin lactones to form FDCN/Fe complexes prevented the intramolecular charge transfer (ICT) process and led to the fluorescence quenching of FDCN. EDTA restored the fluorescence emission of quenched FDCN. The complexation stoichiometry of Fe to FDCN was 1 : 1, and the association constant was 3.23 × 10 M. The high hydrophilicity, sensitivity, and selectivity of FDCN for Fe make the chemosensor suitable for Fe trace detection in drinking water and biology.