Restriction of intramolecular motions (RIM) by metal-organic frameworks for electrochemiluminescence enhancement:2D Zr-adb nanoplate as a novel ECL tag for the construction of biosensing platform.

Herein, a new phenomenon of enhanced electrochemiluminescence (ECL) emission by restricting intramolecular motion in the 2D ultra-thin Zr-adb (adb = 9,10-anthracene dibenzoate) metal-organic framework (MOF) nanoplate was discovered for the first time. The coordination immobilization of adb in porous ultra-thin Zr-adb nanoplate endowed the Zr-adb excellent ECL performance, including stronger ECL signal and higher ECL efficiency relative to those of Hadb monomers and Hadb aggregates. In the 2D Zr-adb nanoplate, the bridging ligand adb was stretched and fixed between two Zr clusters, which restricted intramolecular rotations and suppressed unnecessary energy loss caused by self-rotation, thereby remarkably improved the ECL intensity and efficiency. More importantly, the porous ultra-thin structure of Zr-adb MOF nanoplate not only allowed the coreactants to diffuse into the MOF interior, making both internal and external adb be excited, but also shortened the migration distance of electrons, ions, coreactants and coreactant intermediates, which further improved the ECL efficiency of Zr-adb and overcame the shortcoming of Hadb aggregates in which the internal luminophores were not easily excited. Regarding the excellent ECL properties above, Zr-adb nanoplate was selected as a new ECL emitter incorporated with the bipedal walking molecular machine together to fabricate a biosensor for sensitive detection of mucin 1. The enhanced ECL by restriction of intramolecular motions in MOFs provided a new pathway to improve ECL intensity and efficiency, which lighted up a lamp for the design and manufacture of high-performance ECL materials based on MOFs, thus offering new opportunities to develop ultrasensitive ECL biosensors.