Yellow-emitting carbon dots as 'off-on' fluorescence probes in paper-based micro kit for selective detection of silver ions and kanamycin in animal-derived food

A simple and selective "turn off-on"fluorescent sensor for silver ions (Ag⁺) and kanamycin sulfate (Kana) was developed using bright yellow-fluorescent carbon dots (Y-CDs), synthesized via a one-pot hydrothermal method from o-phenylenediamine (o-PDA) and tris(hydroxymethyl)aminomethane (Tris). Y-CDs showed excellent photoluminescence and stability confirmed by various analytical techniques, including absorption, fluorescence, Fourier-transform infrared (FT-IR), X-ray photoelectron (XPS), Nuclear magnetic resonance (NMR) spectroscopy, high resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), zeta potential, and fluorescence lifetime measurements. The sensing mechanism is based on the principle of fluorescence quenching by Ag⁺ via static quenching and photoinduced electron transfer (PET) process, followed by fluorescence recovery upon Kana binding. The probe showed a linear detection range of 3.33-50 M for Ag⁺ and 6.66-66.6 M for Kana, with limits of detection (LOD) of 48.8 and 51.9 nM, respectively. Its practicality was verified in real water and milk samples, and a low-cost paper-based micro kit for rapid on-site detection was developed, demonstrating the potential of Y-CDs in real sensing applications.