Dye-Encapsulated Lanthanide Metal-Organic Framework as a Ratiometric Fluorescent Sensor for Visual Sensing of Uric Acid.

A novel dual-emission ratiometric fluorescent sensor, Dye@Tb-MOFs, was successfully constructed via a simple post-synthetic method. Using an excitation wavelength of 320 nm, the resulting composite exhibits dual well-resolved emission bands at 440 nm (attributed to the dye) and 545 nm (characteristic of Tb3+ ions), with the fluorescence intensity ratio (I545/I440) serving as a self-calibrating signal. The sensor demonstrates excellent stability over a wide pH range (3-9) and outstanding selectivity for uric acid (UA) in the presence of common urinary components. Upon interaction with UA, the green emission at 545 nm is selectively and significantly quenched, whereas the blue emission at 440 nm remained almost unchanged. As a result, I545/I440 shows a significant reduction, accompanied by a visually discernible fluorescence color change of the test strips under UV light from the original green to blue. A good linear relationship between the ratiometric signal and UA concentration is established in the range of 10-1000 µM, with a detection limit as low as 1.70 µM. In addition, the sensor exhibits satisfactory reusability. The quenching mechanism was attributed to the competitive absorption of excitation energy between the ligand and UA, following the inner filter effect principle. This work presents a highly selective and sensitive ratiometric fluorescent platform for the direct UA detection, showing great potential for biosensing applications.