Benzotrithiophene-based covalent organic frameworks for real-time visual onsite assays of enrofloxacin

Enrofloxacin (ENR) is a fluoroquinolone antibiotic that has been used to treat bacterial diseases in aquaculture extensively. ENR might accumulate in the body and cause severe liver damage. Therefore, it is necessary to develop a method for rapid detection of ENR. Herein, amine monomers with different numbers of amino groups, charge and length (1,3-diaminoguanidine monohydrochloride: DMGH, triaminoguanidine hydrochloride: TAGH, hydrazine: H) were used to regulate the fluorescence of benzotrithiophene tricar-baldehyde (BTT)-based covalent organic frameworks (COFs) for real-time visual onsite assays of ENR for the first time. The C₃ symmetric COF_BTT-TAGH only had one emission peak at 540 nm, while C₆ symmetric COF_BTT-DMGH and COF_BTT-H had two emission peaks. COF_BTT-TAGH could achieve the color transition from green to blue with increasing ENR. Thus test paper and gel were designed as real-time detection tools, combined with a smartphone APP. The detection limits obtained by RGB analysis were 106.2 nM for test paper and 26.00 nM for test gel, respectively. This method was applied to detect ENR in fish and clam metabolite successfully. This work also provides important reference to regulate fluorescence of COFs according to actual application.