Sensitive Ratiometric Fluorescent Metal-Organic Framework Sensor for Calcium Signaling in Human Blood Ionic Concentration Media

A two-dimensional fluorescent metal-organic framework (MOF) sensor, TMU-5S, was synthesized by introducing rhodamine B into the framework of TMU-5. This dye-sensitized MOF was explored as a ratiometric fluorescent sensor for Ca²⁺ signaling in the presence of interfering cations in ionic concentrations similar to that of blood plasma that exhibits exceptional sensitivity and selectivity to Ca²⁺ and faster response and recovery times than any other reported fluorescent sensor. This can be attributed to strong electrostatic interactions between basic azine groups in the narrow pore walls of TMU-5S and Ca²⁺ as hard-hard acid-base interactions. The results show that the two-dimensional signal transduction can reduce interfering responses from the environment and thus create exceptional sensitivity.