Water-Stable Luminescent Eu–Al-Nanoscale Metal–Organic Gels for the Detection of Doxycycline

The rapid detection of antibiotics in water plays a crucial role in environmental monitoring. This paper focuses on the fabrication and synthesis of an Eu–Al-MOG (metal–organic gel, MOG) nanoscale luminescent material using a combination of sol–gel and curing methods, which is suitable for the efficient and repetitive detection of doxycycline (DOX). Structural analysis, including X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy (EDS), verifies the homogeneous and close combination of the luminescent material [Eu-MOF (MOF = metal–organic framework)] and host material (Al-MOG) within the Eu–Al-MOG composite. Eu–Al-MOG exhibits a fluorescence emission at 280 nm, facilitating effective DOX detection through fluorescence quenching. The achieved lowest limit of detection is 0.77 μM. Benefiting from the Al-MOG matrix, the fluorescence emission intensity could exhibit consistent stability during 90 min of continuous detection. In repeated detections, the mass could be preserved, and the emission intensity could be easily recovered through simple rinsing, demonstrating excellent stability and reusability. The detection mechanism of DOX is analyzed as the internal filtration effect and photoinduced electron transfer through fluorescence lifetimes, UV–vis absorption spectra, and other analyses. Furthermore, the study investigates the formation mechanism of Eu2–Al2-MOG composites and proposes an optimal synthesis strategy for their preparation. This work introduces concepts for the sensor design and application of luminescent MOF materials in the field.