Class-selective and highly sensitive detection of β-diketone antibiotics in milk using a Eu(III)-anchored covalent organic framework probe via dual-mode ratiometric strategy.

Developing reliable methods for β-diketone antibiotics detection is significant for food security. Herein, a Eu(III)-anchored COF probe was designed for class-selective and sensitive detection of β-diketone antibiotics via a dual-mode sensor. This Eu(III)@COF probe exhibited inherent fluorescence at 527 nm, served as an internal reference signal. Upon addition of levofloxacin (LVF, a model of β-diketone antibiotics), the resulting LVF-Eu(III)@COF exhibited a markedly enhanced fluorescence at 616 nm due to target-induced "antenna effect". Thus, a ratiometric fluorescent sensor was successfully constructed for LVF detection using the intensity ratio of F616 to F527. Furthermore, a portable smartphone-aided visualization platform was developed for detecting LVF using RGB-based ratio with a LOD of 0.746 μM. The dual-mode ratiometric sensor features self-calibration and cross-verification capabilities, which can minimize interferences from complicated matrices and external fluctuations. This sensor demonstrates a promising approach for class-selective assay of β-diketone antibiotics and accurate detection of LVF in milk samples.