Uranium can enter waterways through mining, fuel processing and waste handling. In water, it commonly occurs as the mobile uranyl ion, making sensitive detection important for environmental monitoring. Laboratory methods can measure uranium at low concentrations, but their cost, sample preparation needs and bulky equipment can limit on-site use.
Fluorescent probes offer a simpler approach; however, those that rely on a single brightness reading can be affected by changes in probe concentration, illumination or the water sample itself. Comparing two emissions offers a way to make readings more reliable.
A study (DOI: 10.48130/scm-0026-0025) published in Sustainable Carbon Materials on 02 September 2026 by Suhua Wang's team, Guangdong University of Petrochemical Technology, reports that a europium-zinc probe converts uranyl binding into opposing red and green fluorescence signals.
The team synthesized a coordination polymer called EuZn-PMA by combining europium and zinc ions with pyromellitic acid, an organic compound bearing carboxyl groups. They then compared it with materials made using only europium or only zinc. Imaging showed that the two-metal material formed relatively uniform microspheres, about 0.5 micrometers across, while the single-metal materials had different, less uniform structures. Spectroscopy confirmed that both metals were incorporated, and fluorescence measurements showed stronger europium emission from EuZn-PMA than from the europium-only material.
Zinc helped organize the structure and enhance its light output, while europium supplied the initial red signal. To test detection, the researchers added increasing amounts of uranyl ions to a suspension of the probe and measured its emissions. The red europium signal at 616 nanometers weakened as a green signal at 513 nanometers appeared. The ratio between the two changed predictably across uranyl concentrations from 0 to 60 micromolar, yielding a calculated detection limit of 51 nanomolar.
Further measurements supported the proposed explanation: uranyl binds to the ligand's carboxyl groups, disrupting the transfer of energy that normally produces red europium fluorescence while generating the green response.The team also tested a range of individual ions that might coexist with uranyl and found limited interference under the conditions studied. In filtered lake water and seawater supplemented with known uranyl concentrations of 1, 2 and 4 micromolar, the probe recovered 94.5% to 102.5% of the added amount. Finally, the researchers photographed illuminated samples with a smartphone. The ratio of green to red values in the images tracked uranyl concentration, demonstrating a possible visual readout without a laboratory fluorescence spectrometer.
Together, the findings show that coordinating europium and zinc in one probe can turn uranyl binding into a measurable red-to-green fluorescence change. Its sensitivity, smartphone readout and performance in spiked lake water and seawater point to potential use in portable water monitoring. Further testing with naturally contaminated samples and mixtures of interfering substances will be needed to determine how reliably the probe performs across the varied conditions encountered in the field.