A novel fluorescence platform for specific detection of tetracycline antibiotics based on [MQDA-Eu³⁺] system

Tetracycline antibiotics (TCs) are extensively used in clinical medicine, animal husbandry, and aquaculture because of their cost-effectiveness and high antibacterial efficacy. However, the presence of TCs residues in the environment poses risks to humans. In this study, an inner filter effect (IFE) fluorescent probe, 2,2'-(ethane-1,2-diylbis((2-((2-methylquinolin-8-yl)amino)-2-oxoethyl)azanediyl))diacetic acid (MQDA), was developed for the rapid detection of Eu³⁺ within 30 s. And its complex [MQDA-Eu³⁺] was successfully used for the detection of TCs. Upon coordination of a carboxyl of MQDA with Eu³⁺ to form a [MQDA-Eu³⁺] complex, the carboxyl served as an antenna ligand for the effective detection of Eu³⁺ to intensify the emission intensity of MQDA via "antenna effect", the process was the energy absorbed by TCs via UV excitation was effectively transferred to Eu³⁺. Fluorescence quenching of the [MQDA-Eu³⁺] complex was caused by the IFE in multicolor fluorescence systems. The limits of detection of [MQDA-Eu³⁺] for oxytetracycline, chlorotetracycline hydrochloride, and tetracycline were 0.80, 0.93, and 1.7 μM in DMSO/HEPES (7:3, v/v, pH = 7.0), respectively. [MQDA-Eu³⁺] demonstrated sensitive detection of TCs in environmental and food samples with satisfactory recoveries and exhibited excellent imaging capabilities for TCs in living cells and zebrafish with low cytotoxicity. The proposed approach demonstrated considerable potential for the quantitative detection of TCs.