Recently, a research team led by Prof. JIANG Changlong from the Institute of Solid State, Hefei Institutes of Physical Science (HFIPS) of the Chinese Academy of Sciences (CAS) used the coordination polymerization of europium ion (Eu3+) and 3,5-dicarboxyphenylboronic acid (BBDC) to construct a multi-emitting europium metal organic framework fluorophore, which was used for the visual detection of gallic acid (GA) through a portable sensing platform.

They designed and synthesized dual-emission Europium Metal-Organic Frameworks (Eu-MOF) fluorescent probes through the covalent binding and enrichment of GA in tea and fruit juice, and proposed an effective food additive monitoring strategy.

The paper was published in Chemical Engineering Journal.

Gallic acid (GA) has various biological activities because of its reducing properties in tea and fresh fruit juice. It has an antioxidation effect in humans through its scavenging reactive oxygen species (ROS) and other free radical ions, and has ability to significantly reduce the ROS index. GA is not only found naturally in green tea, black tea and many other plants, but also widely applicate in food and health care products because of the strong antiradical activity and antioxidant effect. The rapid and visual detection of GA is of great significance to analytical chemistry.

In this research, based on the polymerization of boronic acid-based ligands and europium metal ions, researchers developed a multi-emission Eu-MOF under single-wavelength excitation for rapid visual detection of GA, and used a smartphone APP (color identifier) to identify fluorescent probe solutions.

The Red-Green-Blue (RGB) value of the color completed the visual detection of GA.

After the introduction of boronic acid groups, Eu-MOF had two emission centers under single-wavelength excitation. When GA was detected, the emission color of Eu-MOF changed from red to blue under a UV lamp, which was caused by a shift in energy transfer efficiency in Eu-MOF.

This multi-emission Eu-MOF exhibited remarkable luminescence properties, high sensitivity, fast visual response to GA, good dispersion and low detection limit in detection, which could be used in practical samples such as tea and fruit juices.

The visual detection can be performed when combined with the fluorescence sensing platform prepared by smartphone.

"This designed method provided new ideas and approaches for the development of food quality control evaluation systems," said PAN Lei, first author of the paper, "and was expected to expand the application of multi-emission Eu-MOFs in the fields of chemical and analytical sensing."

This research work was supported by the National Natural Science Foundation of China, the National Key Research and Development Program of China and the Key Research and Development Program of Anhui Province.