Microplasma-fabricated CDs@Eu-DPA for ratiometric fluorescence and smartphone-mediated visual detection of oxytetracycline in food samples

A dual-emission CDs@Eu-DPA composite was rapidly synthesized via dielectric barrier discharge microplasma technology using carbon dots (CDs), 2,6-dipicolinic acid (DPA), and Eu 3+ as precursors. CDs@Eu-DPA was subsequently applied for ratiometric fluorescence and visual analysis of oxytetracycline (OTC) in food samples. When OTC was introduced, the blue fluorescence of CDs was quenched via the inner filter effect, while OTC coordinated with Eu 3+ in Eu-DPA to form a complex, leading to the enhancement of the red fluorescence of Eu 3+ at 615 nm through antenna effect. Additionally, principal component analysis was employed to distinguish four different antibiotics, including OTC, chlortetracycline, tetracycline, and doxycycline. Under optimized conditions, the ratiometric fluorescence analysis and smartphone-assisted RGB analysis exhibited linear detection ranges of 0.05–210.0 μM and 0.3–90.0 μM for OTC, respectively, with limits of detection of 0.02 μM and 0.08 μM, respectively. The satisfactory recoveries in food samples were ultimately achieved through the dual-mode sensing method.