Tetracycline (TC) is an antibiotic that has been widely used in the animal husbandry. Thus, TC residues may be found in animal products. Developing simple and sensitive methods for rapid screening of TC in complex samples is of great importance. Herein, we demonstrate a fluorescence-sensing method using Zn2+ as sensing probes for the detection of TC. Although TC can emit fluorescence under the excitation of ultraviolet light, its fluorescence is weak because of dynamic intramolecular rotations, leading to the dissipation of excitation energy. With the addition of Zn2+ prepared in tris(hydroxymethyl)amino-methane (Tris), TC can coordinate with Zn2+ in the Zn2+-Tris conjugates to form Tris-Zn2+-TC complexes. Therefore, the intramolecular motions of TC are restricted to reduce nonradiative decay, resulting in the enhancement of TC fluorescence. Aggregation-induced emission effects also play a role in the enhancement of TC fluorescence. Our results show that the linear dynamic range for the detection of TC is 15–300 nM. Moreover, the limit of detection was ~7 nM. The feasibility of using the developed method for determination of the concentration of TC in a complex chicken broth sample is also demonstrated in this work.

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Tetracycline (TC) is a broad-spectrum antibiotic and has been added to animal feeds to grow livestock under healthy conditions, making it important to have effective methods for rapidly detecting TC in complex samples. In this study, a novel method that uses lanthanide ions (i.e. Eu 3+ and Gd 3+ ) as magnetic and sensing probes for the detection of TC from aqueous samples is explored. When dissolving Gd 3+ in tris(hydroxymethyl)aminomethane (Tris) buffer at pH 9, magnetic Gd 3+ -Tris conjugates can be readily generated. The magnetic Gd 3+ -Tris conjugates possess trapping capacity toward TC from sample solutions via the chelation of Gd 3+ and TC. Eu 3+ is used as the fluorescence sensing probe against TC on the Gd 3+ -TC conjugates via the antenna effect. The fluorescence response derived from Eu 3+ is increased with the increase of TC trapped on the Gd 3+ -based probes. The linear dynamic range against TC ranges from 20 to 320 nM, whereas the limit of detection toward TC is ~2 nM. Furthermore, the developed sensing method can be employed for the visual assay of TC with a concentration above ~0.16 μM under UV light illumination in the dark. Furthermore, we have demonstrated the applicability of the developed method to quantify TC in a chicken broth sample with complex matrix. Our developed method offers several advantages, including high sensitivity and good selectivity, for the detection of TC in complex samples.