Highly Stable Covalent Organic Framework Nanosheets\nas a New Generation of Electrochemiluminescence Emitters for Ultrasensitive\nMicroRNA Detection

Abstract

A pyrene-based\nsp² carbon-conjugated covalent organic\nframework (COF) nanosheet (Py-sp²c-CON) with strong and\nstable electrochemiluminescence (ECL) emission was constructed by\nCC polycondensation of tetrakis­(4-formylphenyl)­pyrene (TFPPy)\nand 2,2′-(1,4-phenylene)­diacetonitrile, which was employed\nas a highly efficient ECL emitter to fabricate an ECL biosensor for\nthe first time. The Py-sp²c-CON exhibited higher ECL intensity\nand efficiency than those of TFPPy, bulk Py-sp²c-COF, and\nimine-linked pyrene COF, not only because the pyrene luminophores\nand aggregation-induced emissive luminogens (cyano-substituted phenylenevinylene)\nwere topologically linked into Py-sp²c-CON, which greatly\nincreased the immobilization amount of luminophores and decreased\nthe aggregation-caused quenching effect and nonradiative transition\nbut also because the porous ultrathin structure of Py-sp²c-CON effectively shortened transport distances of an electron, ion,\nand co-reactant (S₂O₈^2–),\nwhich made more ECL luminophores be activated and thus efficiently\nincreased the utilization ratio of luminophores. More interestingly,\nwhen Bu₄NPF₆ was introduced into the Py-sp²c-CON/S₂O₈^2– system\nas a co-reaction accelerator, the ECL signal of Py-sp²c-CON\nwas further amplified. As expected, the average ECL intensity of the\nPy-sp²c-CON/S₂O₈^2–/Bu₄NPF₆ system was about 2.03, 5.76, 24.31,\nand 190.33-fold higher than those of Py-sp²c-CON/S₂O₈^2–, Py-sp²c-COF/S₂O₈^2–, TFPPy/S₂O₈²,^– and imine-linked pyrene COF/S₂O₈^2– systems. Considering these\nadvantages, the Py-sp²c-CON/S₂O₈^2–/Bu₄NPF₆ system was employed\nto prepare an ECL biosensor for microRNA-21 detection, which exhibited\na broad linear response (100 aM to 1 nM) and a low detection limit\n(46 aM). Overall, this work demonstrated that sp² carbon\nCONs can be directly used as a high-performance ECL emitter, thus\nexpanding the application scope of COFs and opening a new horizon\nto develop new types of ECL emitters.