Eu-polyaspartic acid based ratiometric fluorescent probes for ultrasensitive and visual detection of tetracycline and copper ions in food samples

The visualization and accurate on-site detection of tetracycline and Cu²⁺ residues in food are essential for maintaining food safety and public health. A novel poly (aspartic acid) Ratiometric fluorescent probe was designed for the sensitive visual detection of tetracycline (Tc) and Cu²⁺ using the EDTA-Eu³⁺ complex as the sensing unit and fluorescein dye as the internal standard. The fluorescence of Eu³⁺ at 617 nm was turned on significantly by Tc via the “antenna effect” and can be quenched by Cu²⁺ owing to the inner filter effect. The probes selectively detected Tc and Cu²⁺ over a wide linear range, low LODs of 10 nM and 333 nM, respectively, were obtained. A smartphone APP and probe-loaded test paper were also assembled into a biomass-based portable sensor for visual point-of-use analysis. The fabricated sensors successfully monitored the Tc and Cu²⁺ levels in milk, honey, and tap water samples, suggesting their broad applications in food safety monitoring and environmental analysis.