Dual-functional fluorescent composite based on carbon dots‑europium ions: intelligent ratiometric detection and adsorption of tetracyclines.

Residual tetracycline antibiotics (TCs), especially tetracycline (TC) and doxycycline (DOX), pose critical threats to ecosystems and human health. There is an urgent demand for approaches capable of rapid, on-site monitoring and removal of TCs. Herein, a ratiometric fluorescent hybrid probe (HA-CDs/Eu3+) was engineered by integrating HA-CDs with Eu3+, featuring specific fluorescence response toward TCs (superior sensitivity to TC and DOX) and adsorption capacity. Upon the introduction of TC, quenching of the blue emission of HA-CDs occurred via the inner filter effect (IFE), while the red emission of Eu3+ was considerably sensitized through the antenna effect (AE). Leveraging opposite response signals, the HA-CDs/Eu3+ probe enabled the ratiometric quantification of TC over a linear range of 0.05-70 μM, achieving a detection limit (LOD) as low as 32 nM. Meanwhile, the probe exhibited an ultra-low LOD of 15 nM for DOX. The practicality of the probe was validated in the Fenhe River water and honey samples, demonstrating excellent recoveries and reproducibility. Furthermore, a smartphone-integrated detection device was developed, in which fluorescent nanopaper was employed to record the color response ratio for the visual detection of TC/DOX in the samples. In addition, the composite was incorporated into hydrogel microspheres, combining their optical advantages with hydrogel properties, which could not only act as an optical sensor for TC recognition, but also exhibit adsorption capacity for TC removal. This work provides an intelligent platform for the quantification and removal of TCs, holding great promise for on-site monitoring of environmental tetracycline pollutants in resource-limited settings.