Fluorescence Visualization Quantitative Detection of Tetracycline and Nitrofurantoin in Food and Natural Water by Zn²⁺@Eu-bpdc Composite

Quantitative detection of tetracycline (TC) and nitrofurantoin (NFT) in food and water is of importance for food safety and environmental protection. Herein, Zn²⁺ was introduced into a europium metal-organic framework Eu-bpdc (H₂bpdc = 2,2'-bipyridyl-5,5'-dicarboxylic acid) to prepare a composite of Zn²⁺@Eu-bpdc, which was developed as a fluorescence sensor for TC and NFT. The fluorescence mechanism concerns with bpdc^2- ligand-to-Eu(III) charge transfer, and the detection mechanism is the inner filter effect. Zn²⁺@Eu-bpdc is a ratiometric fluorescence sensor for TC with the linear fitting equation of <i>I</i>₅₂₀/<i>I</i>₆₁₈ = 1.94 × 10⁴ M^-1<i>C</i>_TC, whose limit of detection (LOD) is 0.148 μmol·L^-1 (μM); it is also a fluorescence "turn-off" sensor for NFT with the fitting equation of (<i>I</i>₀-<i>I</i>)/<i>I</i> = 3.62 × 10⁴ M^-1<i>C</i>_NFT and LOD = 0.0792 μM. Zn²⁺@Eu-bpdc can detect TC or NFT in lake water, honey, and milk with high accuracy. The emission color changes of paper-based Zn²⁺@Eu-bpdc depending on <i>C</i>_TC or <i>C</i>_NFT reveal the visualization detections of TC and NFT. With the red and green values as input signals, smartphone-assisted on-site detection is utilized to recognize the antibiotic residuals of TC and NFT by a self-programmed APP. Zn²⁺@Eu-bpdc is promising in a smartphone-assisted intelligent platform for on-site detection of TC and NFT.