Highly Stable Covalent Organic Framework Nanosheets as a New Generation of Electrochemiluminescence Emitters for Ultrasensitive MicroRNA Detection

A pyrene-based sp(2) carbon-conjugated covalent organic framework (COF) nanosheet (Py-sp(2)c-CON) with strong and stable electrochemiluminescence (ECL) emission was constructed by C=C polycondensation of tetrakis(4-formylphenyl)pyrene (TFPPy) and 2,2'-(1,4-phenylene)- diacetonitrile, which was employed as a highly efficient ECL emitter to fabricate an ECL biosensor for the first time. The Py-sp(2)c-CON exhibited higher ECL intensity and efficiency than those of TFPPy, bulk Py-sp(2)c-COF, and imine-linked pyrene COF, not only because the pyrene luminophores and aggregation-induced emissive luminogens (cyano-substituted phenylenevinylene) were topologically linked into Py-sp(2)c-CON, which greatly increased the immobilization amount of luminophores and decreased the aggregation-caused quenching effect and nonradiative transition but also because the porous ultrathin structure of Py-sp(2)c-CON effectively shortened transport distances of an electron, ion, and co-reactant (S2O82-), which made more ECL luminophores be activated and thus efficiently increased the utilization ratio of luminophores. More interestingly, when Bu4NPF6 was introduced into the Py-sp(2)c-CON/S2O82- system as a co-reaction accelerator, the ECL signal of Py-sp(2)c-CON was further amplified. As expected, the average ECL intensity of the Py-sp(2)c-CON/S2O82-/Bu4NPF6 system was about 2.03, S.76, 24.31, and 190.33-fold higher than those of Py-sp(2)c-CON/S2O82-, Py-sp(2)c-COF/S2O82-, TFPPy/S2O82-, and imine-linked pyrene COF/S2O82- systems. Considering these advantages, the Py-sp(2)c-CON/S2O82-/Bu4NPF6 system was employed to prepare an ECL biosensor for microRNA-21 detection, which exhibited a broad linear response (100 aM to 1 nM) and a low detection limit (46 aM). Overall, this work demonstrated that sp(2) carbon CONs can be directly used as a high-performance ECL emitter, thus expanding the application scope of COFs and opening a new horizon to develop new types of ECL emitters.

Automated summary

A novel pyrene-based sp(2) carbon-conjugated covalent organic framework nanosheet was constructed, exhibiting strong and stable electrochemiluminescence emission for the first time. The Py-sp(2)c-CON showed higher ECL intensity and efficiency compared to other materials, and when combined with Bu4NPF6, the ECL signal was further amplified, allowing for the detection of microRNA-21 with broad linear response range and low detection limit. Overall, this work demonstrates the potential of sp(2) carbon COFs as high-performance ECL emitters with expanded applications in biosensing.