Eu doped carbon dots as a ratiometric fluorescence probe for highly sensitive detection of trace tetracycline in milk.

The Eu-doped carbon dots (CDs-Eu) with high sensitivity and ratiometric fluorescence property is constructed as a luminescence probe for detection of tetracycline (TC). The as-prepared probe emits intrinsic blue fluorescence at 443 nm (quantum yield: 8.7%), characteristic of carbon dots (CDs). In the presence of TC, the probe demonstrate a dual response mechanism: the blue fluorescence of probe is selectively quenched via inner filter effect (IFE). Simultaneously, the TC induced antenna effect enhances the characteristic Eu emission at 620 nm through chelation. The ratio of fluorescence intensity I/I increases linearly in the TC concentration range of 0.01 μM to 240 μM with low detection limit of 3.83 nM. The probe exhibits remarkble sensitivity and selectivity, successfully applied in TC detection from milk samples with recoveries between 97.70 and 104.9%. This approach lays the groundwork for detecting multiple antibiotic residues across various samples. Furthermore, to facilitate practical applications, we constructed a sensing system utilizing smartphones which enables rapid, facile, and visual TC detection, which may offer a promising utilization for real-time and semi-quantitative assay of TC.