Construction of Zinc-based metal-organic frameworks for visual ratiometric fluorescence detection of tetracycline

Tetracycline (TC) is frequently utilized as additives in animal feed. The misuse can lead to the residue in food and threaten human health.

A ratiometric fluorescence method for tetracycline detection is developed based on Zinc-based metal-organic framework (Zn-MOF) materials. A series of Zn-MOFs are synthesized with phthalic acid derivatives as ligand, and their luminescence properties and interaction with tetracycline are investigated. Thereinto, Zn-BDC-OH MOF synthesized with 2-hydroxyterephthalic acid (BDC-OH) as ligand exhibits sensitive fluorescence response to tetracycline. The blue fluorescence of Zn-BDC-OH at 434 nm is quenched by tetracycline due to inner filter effect (IFE), and the green fluorescence of TC at 531 nm is enhanced because of coordination with Zn²⁺. The fluorescence intensity ratio I₅₃₁/I₄₃₄ shows a linear relationship with TC concentration in the range of 0.10-40.0 μM with a limit of detection at 79 nM. The fluorescence colors of Zn-BDC-OH MOF change from blue to cyan to green accompanying with increasing TC concentration, which enables the visual and semi-quantitative detection of tetracycline by naked eyes. Moreover, combined with a smartphone, the RGB value of the fluorescence color can be further identified. The ratio (G/B) of green channel to blue channel shows a linear relationship with the TC concentration in the range of 0.25-25.0 μM with a limit of detection at 0.2 μM. Afterwards, Zn-BDC-OH MOF is successfully applied to detect tetracycline in honey, and the results are consistent with those obtained from chromatography.

The established method exhibits great potential for field visualization and rapid detection of tetracycline.