Using lanthanide ions as magnetic and sensing probes for the detection of tetracycline from complex samples.

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. Eu³⁺ and Gd³⁺) as magnetic and sensing probes for the detection of TC from aqueous samples is explored. When dissolving Gd³⁺ in tris(hydroxymethyl)aminomethane (Tris) buffer at pH 9, magnetic Gd³⁺-Tris conjugates can be readily generated. The magnetic Gd³⁺-Tris conjugates possess trapping capacity toward TC from sample solutions via the chelation of Gd³⁺ and TC. Eu³⁺ is used as the fluorescence sensing probe against TC on the Gd³⁺-TC conjugates via the antenna effect. The fluorescence response derived from Eu³⁺ is increased with the increase of TC trapped on the Gd³⁺-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.