Sour taste sensor based on multiply functionalized hydrogen-bonded organic frameworks for identifying organic acids in food by combining phosphorescence and fluorescence signals

Taste sensor have been receiving increasing attention for the perception of five basic tastes. In particular, sour taste sensor is generally associated with the detection of the maturation degree of fruits and vegetables. Nevertheless, it is still challenging to design a simple sour taste sensor for taste sour substances. To enrich photoluminescent pathways of the sensor, we incorporated organic phosphors (1,3,5-benzenetricarboxylic acid, BTA) and lanthanide ions (Eu³⁺ and Tb³⁺) within hydrogen-bonded organic frameworks (HOF MCA) through in-situ synthesis. The multiple functionalized material EuTb-MCABTA (EuTb-1) can exhibit red and green fluorescent emissions as well as deep-blue phosphorescent emission. EuTb-1 is capable to identify four kinds of organic acids (citric acid, oxalic acid, malic acid and fumaric acid) in food based on multiple photo-responsive signals. By adjusting excitation wavelength, the sour taste sensor further collected the characteristic “portrait” of each analyte, and quantitatively detected them with high sensitivity (10⁻⁷ M). In addition, we investigated the discrepant sensing mechanism based on multiple photoluminescent process, which resulted in the different photo-responses by analytes. This work offers a simple strategy to develop the sour taste sensor with multiple photo-responses and conducts preliminary exploration for the application of phosphorescence materials.