A new hydrazone-linked covalent organic framework for Fe(III) detection by fluorescence and QCM technologies

Since Fe(III) ions are of importance in biological systems, the development of new sensors for detecting Fe(III) with excellent selectivity and low detection limit is desirable. Herein, a new stable hydrazone-linked covalent organic framework (COF), namely, Tfpa–Mth COF, was synthesized by the Schiff-base condensation reaction between tris(4-formylphenyl) amine (Tfpa) and a chiral hydrazide precursor (Mth). The ethanol-dispersed Tfpa–Mth COF can be used as a fluorescence sensor for the detection of Fe(III) ions, showing high selectivity and low detection limit (64 nM). Moreover, a novel COF-based quartz crystal microbalance (QCM) sensor has been fabricated by the in situ growth of the Tfpa–Mth COF on an amino-modified QCM chip. Such a COF-based QCM sensor, with a uniform surface and thickness of the Tfpa–Mth COF film on the surface, is able to monitor Fe(III) ions in real-time with high selectivity. The recognition process, as a result of Fe(III) immobilization on the Tfpa–Mth COF framework, is further verified by zeta potential measurements and X-ray photoelectron spectroscopy. To the best of our knowledge, this represents the first report on the development of COF-based QCM sensors for metal ion detection. Exploration of the COF-based QCM sensor in our work demonstrates the new pathway for the selective detection of metal ions.