A fluorescent Zn(II) metal−organic framework sensor for quantitative tetracycline determination

Tetracyclines (TET) are a group of broad-spectrum antibiotics that have greatly benefited the medical community and the raising of animals. However, the excessive release of TET poses a major risk to human health. The quantitative TET determination is therefore crucial for maintaining good health. Here, we show a 3D PtS topological Zn(II) metal-organic framework based fluorescence sensor for quantitative TET measurement, formulated as {[Zn(2,6-NBC)(H2O)]•0.5(H2O)}n (1) (2,6-H2NBC = 2,6-naphthalenedicarboxynlic acid). The photoluminescence results indicate that 1, with a superior fluorescence quenching constant Ksv of 3.15 × 104 M−1, could be used as a potential fluorescent "turn-off" sensor for quantitative TET measurement in a water-ethanol solution. With increasing TET concentration, the fluorescence quenching activity was consistent with a noticeable shift in color from dark to light blue. In addition, a linear association between the fluorescence emissions and low TET concentrations of 0–40 μM could also be observed, and the detection limit can reach as low as 70 nM, much lower than the maximum residue limits of TC in milk defined by the U.S. Food and Drug Administration (FDA) with the value of 900 nM and the European Union (EU) with the value of 225 nM. In order to make TET determination visibly easier, fluorescent test papers and portable luminous hydrogels have also been developed. The fluorescence resonance energy transfer (FRET) may account for the fluorescence quenching behavior of 1 for TET determination.