Stepwise Assembly of “Turn‐on” Fluorescent Sensors in Multicomponent Metal–Organic Frameworks for in vitro Cyanide Detection

The controlled synthesis of multicomponent MOFs allows for the precise placement of multiple corporative functional groups within a framework, leading to emergent synergistic effects. Herein, we demonstrate that "turn-on" fluorescent sensors can be assembled by combining a fluorophore and a recognition moiety within a complex cavity of a multicomponent MOF. An anthracene-based fluorescent linker and a hemicyanine-containing CN- responsive linker were sequentially installed into the lattice of PCN-700. The selective binding of CN- to hemicyanine inhibited the energy transfer between the two moieties, resulting in a fluorescence "turn on" effect. Taking advantage of the high tunability of the MOF platform, the ratio between anthracene and the hemicyanine moiety could be fine-tuned in order to maximize the sensitivity of the overall framework. The optimized MOF-sensor had a CN- detection limit of 0.05 muM, which is much lower than traditional CN- molecular fluorescent sensors (~0.2 muM).