Red-to-blue fluorescent switching in Eu-MOG nanofibrous membranes for visual and ratiometric detection of amikacin in dairy products

A Eu-MOG@PAN nanofibrous membrane was fabricated for amikacin sensing. • Amikacin induces red-to-blue fluorescence switching in the solid-state membrane. • Ratiometric detection is achieved without an additional reference fluorophore. • The membrane shows high selectivity with a detection limit of 0.38 μM. • Amikacin in whey was successfully determined by visual and fluorescence analysis. Lanthanide metal–organic materials are attractive for optical sensing, but their application in complex aqueous samples is often hindered by single-channel emission, poor processability and insufficient signal reliability. Herein, we report a flexible mixed-matrix nanofibrous membrane fabricated by confining a europium metal–organic gel (Eu-MOG) within an electrospun polyacrylonitrile (PAN) scaffold. The membrane enables amikacin-triggered ratiometric luminescence sensing via nanoscale interfacial coordination. Upon exposure to amikacin, the amino groups of amikacin coordinate to Eu 3+ sites, perturb the Eu–carboxylate microenvironment and weaken the antenna effect, resulting in strong quenching of the Eu 3+ emission and simultaneous recovery of ligand-centred blue emission at 458 nm. This red-to-blue transformation provides a built-in ratiometric readout (I₄₅₈/I₆₁₉) without the need for an additional reference fluorophore. Control experiments confirm that the 458 nm emission originates from the organic ligand rather than from amikacin or PAN. Mechanistic studies based on fluorescence lifetimes, FT-IR, XPS, zeta-potential and spectral overlap reveal that the response is dominated by amikacin–Eu 3+ coordination and the consequent disruption of ligand-to-Eu 3+ energy transfer. The electrospun membrane offers an open, mechanically robust architecture that facilitates analyte access and solid-state operation. It exhibits high selectivity for amikacin over common inorganic ions, amino acids, and other antibiotics. The ratiometric response is linear over the low-concentration range of 1–9 μM, while the response at 10–100 μM can be described using a Logistic fitting model. The calculated limit of detection is 0.38 μM. The method was successfully applied to the determination of amikacin in whey samples with good reproducibility. This work presents a ligand-emission activation strategy for constructing lanthanide-based ratiometric nanofibrous membranes and demonstrates a portable platform for visual screening of antibiotic residues in dairy products. Download: Download high-res image (286KB) Download: Download full-size image