Ratiometric fluorescent probes based on carbon dots and europium for rapid detection of tetracycline

Tetracycline (TC) is a typical emerging pharmaceuticals and personal care products (PPCPs) pollutants in the environment. However, TC residues cause severe effects on human health. It is crucial to exploit simple, rapid and sensitive methods to detect TC in water samples. A ratiometric fluorescent probes (CDs-Eu3+) is constructed using carbon dots (CDs) and europium ions (Eu3+) for the visual detection of tetracycline (TC). Under 390 nm excitation, CDs-Eu3+ shows a strong yellow fluorescence at 545 nm and a weak red fluorescence at 619 nm, respectively. In the presence of TC, the fluorescence intensity at 545 nm decreased while the fluorescence intensity at 619 nm increased, which attributed to the internal filtering effect (IFE) and "antenna effect", respectively. Sensing performance of CDs-Eu3+ probes is further evaluated with respect to various conditions, including salt concentration, Eu3+ concentration, pH, and reaction time. Results reveal that the proposed ratiometric fluorescent probes exhibits a specific recognition ability toward TC. An excellent linear relationship is observed between the fluorescence intensity ratio (F619/F545) and TC concentrations (1⁓100 μM), with a low detection limit (LOD) of 31 nM. The solution (CDs-Eu3+-TC) color gradually changes from yellow to red after adding TC. The probes are successfully applied to determine TC in water with recoveries of 85.43⁓97.53%. Finally, a fluorescent test strip is prepared and used for rapid visual semi-quantitative TC detection.