Lanthanide-grafted covalent organic framework as a colorimetric and luminescence dual-mode nanoprobe for tetracycline detection

Tetracyclines (TCs) are a group of antibiotics commonly using for infection treatment, however, the leftovers in potable water and food which are derived from the abuse of TCs lead to the adverse human health and environmental impacts. Herein, we developed a lanthanide-grafted covalent organic framework (COF) as a colorimetric and luminescence dual-mode nanoprobe to realize precise, sensitive, rapid, real-time TC determination. Ce3+, Eu3+ ions were chosen to functionalize COFs due to their particular corresponding catalytic and luminescent characteristic for bimodal sensing. COF-Ce-Eu can work as an enzyme mimic to catalytically oxidize the substrate of 3,3',5,5'-tetramethylbenzidine (TMB) with existence of H2O2, besides, the addition of TC is conducive to promote the pristine catalytic activity as the formation of complexation of COF-Ce-Eu with TC. The catalytic activity and the absorbance of COF-Ce-Eu directly correlate to TC concentration. The ratiometric luminescence response was established on the intensity ratio of the broad band centered at 512 nm originated from the matrix COF and the sharp peak at 616 nm originated from Eu3+. The decrease in luminescence intensity of the peak at 512 nm and the increase at 616 nm depended on TC concentration. This colorimetric and luminescence dual-mode platform exhibits excellent selectivity and sensitivity towards TC, with a wide linear range of 0-50 μM, and low detection limits of 24 nM and 3.4 nM, respectively. The designed bimodal sensing strategy provide a promising double assurance for the accurate trace of TC in food and water samples.