Preparation of CQDs/Eu³⁺ Ratiometric Fluorescent Probe for Visual Detection of Tetracycline

A ratiometric fluorescent probe was constructed with carbon quantum dots (CQDs) and europium ions (Eu³⁺) as a fluorophore for the visual detection of teracycline (TC). In this ratiometric probe, CQDs/Eu³⁺ has an intense blue fluorescence peak at 439 nm and a weak red fluorescence peak at 616 nm under the excitation of 380 nm wavelength. The fluorescence peak intensity of CQDs at 439 nm gradually decreases based on the inner filter effect. The fluorescence intensity of Eu³⁺ at 616 nm increases due to an antenna effect with the addition of TC. The experimental factors, such as CQDs and Eu³⁺ ratio, response time, stability, etc., were optimized. The results show that the ratio fluorescent probe has a specific recognition ability for TC. A linear relationship between the fluorescence intensity ratio(F₆₁₆/F₄₃₉) and different concentrations of TC (0–50 μM) was established with a detection limit of 0.68 µM. With the addition of TC, the color of the ratio fluorescent probe solution under ultraviolet light gradually changes from blue to red and is used for the detection of TC in milk with the recoveries ranging from 92.5% to 1 14.8%. In addition, a TC test paper was also prepared, which can be quickly used for a visual test paper detection of TC.