Covalent Organic Framework Functionalized with Fluorescein Isothiocyanate for the Selective and Sensitive Detection of Toxic Mycotoxin

Staining of foods by toxic mycotoxins is a general severe problem in the world. To explore simple methods for effective monitoring of mycotoxin-stained foods has extraordinary significance. Herein, we designed and prepared a covalent organic framework (COF)-derived fluorescent composite (DhBd-PT-COF-FITC) by anchoring a continually utilized fluorescent tag, fluorescein isothiocyanate (FITC), in the nanopore channel of a two-dimensional imine COF (DhBd-PT-COF) to detect a major existent mycotoxin of moldy sugar cane─3-nitropropionic acid (3-NPA), which is closely related to toxicosis events of humans. Tying FITC molecules into the pore channels of DhBd-PT-COF can not only enhance the fluorescence intensity of FITC by relying on the confinement effect of DhBd-PT-COF but also retain inherent pH-responsive characteristics. As a result, DhBd-PT-COF-FITC showed the selective and sensitive response to 3-NPA. The detection limit of DhBd-PT-COF-FITC toward 3-NPA is achieved to be ultralow as 12.5 nM. More attractively, facile recovery of DhBd-PT-COF-FITC can be obtained via simple alkaline treatment. The prepared sensor has also been used to detect 3-NPA in actual sugar cane samples with satisfying recovery. Our work not only exhibits fascinating performance of COF-derived fluorescent composites toward 3-NPA monitoring but also offers a prospective approach to develop various specific materials for other targets.