Fluorescence sensor based on optimized quantum yield manganese-carbon polymer dots and smartphone-integrated sensing platform for tetracycline detection

The one-step synthesis of Mn-doped carbon quantum dots (Mn-CPDs) with a high quantum yield (QY = 45%) is reported using the microwave-assisted method. Subsequently, Mn-CPDs were successfully combined with Eu³⁺ ions to construct an Eu³⁺@Mn-CPDs fluorescence sensor. The presence of tetracycline (TC) induced a transition of fluorescence emission from blue (434 nm) to red (618 nm), and a robust linear relationship was observed between the ratio of F_{618 nm} / F_{434 nm} and the TC concentration (5 − 50 nmol/L), with a limit of detection (LOD) of 5.76 nmol/L. The underlying mechanism of Eu³⁺@Mn-CPDs and TC sensing is unveiled as a synergistic effect involving inner filter effect (IFE) and concurrent interactions. Notably, the smartphone-integrated sensing platform based on Eu³⁺@Mn-CPDs enables rapid and quantitative TC detection within a short time (< 30 s) by monitoring fluorescence color changes, achieving high-detection sensitivities (with a LOD of 6.18 nmol/L). This versatile and efficient sensing platform demonstrates its potential for the determination of TC concentrations in milk, honey, and tap water samples.