Rapid Determination of Tetracycline Utilizing a ratiometric fluorescence with Co-Doped Carbon Quantum Dots

This study successfully synthesized high performance blue emissive carbon dots (ZrN-CDs) using citric acid, zirconium chloride, and ethylenediamine as precursors through a hydrothermal method. The resulting ZrN-CDs exhibit excitation-independent emission characteristics, along with good water solubility, salt resistance, and photobleaching resistance. The fluorescence resonance energy transfer (FRET) mechanisms allow for the selective attenuation of ZrN-CD fluorescence by tetracyclines (TCs). Building on this effect, a dual-emission ratiometric fluorescent sensor was developed by integrating europium ions (Eu 3+ ), featuring an inverse fluorescence signal response to enhance detection accuracy through self-calibration. The fluorescence emission behavior of ZrN-CDs (F 440 ) showed selective quenching in response to TCs, while the characteristic emission of Eu 3+ (F 615 ) exhibited fluorescence enhancement due to the antenna effect (AE). Quantification of common TCs antibiotics, including tetracycline (TET) and oxytetracycline (OTC), was achieved by recording the fluorescence intensity ratio (F 615 /F 440 ). The limits of detection (LOD) for TET and OTC reached 0.029   μM and 0.016   μM, respectively. This method was successfully applied to the detection of TET in bovine, goat, and camel milk, with recovery rates ranging from 83.65% to 106.60%, thereby confirming the reliability and effectiveness of the sensor in practical applications.