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

Abstract

A pyrene-based sp2 carbon-conjugated covalent organic framework (COF) nanosheet (Py-sp2c-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-sp2c-CON exhibited higher ECL intensity and efficiency than those of TFPPy, bulk Py-sp2c-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-sp2c-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-sp2c-CON effectively shortened transport distances of an electron, ion, and co-reactant (S2O8 2–), 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-sp2c-CON/S2O8 2– system as a co-reaction accelerator, the ECL signal of Py-sp2c-CON was further amplified. As expected, the average ECL intensity of the Py-sp2c-CON/S2O8 2–/Bu4NPF6 system was about 2.03, 5.76, 24.31, and 190.33-fold higher than those of Py-sp2c-CON/S2O8 2–, Py-sp2c-COF/S2O8 2–, TFPPy/S2O8 2,– and imine-linked pyrene COF/S2O8 2– systems. Considering these advantages, the Py-sp2c-CON/S2O8 2–/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 sp2 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.

Intrareticular charge transfer regulated electrochemiluminescence of donor–acceptor covalent organic frameworks

“…Different from metal-organic frameworks that metal nodes might quench the ECL, the covalent organic frameworks (COFs) are a class of metal-free crystalline porous materials and could be applied as ECL emitters 13 . Due to the predesignable nature of COFs 14 , 15 , their charge transfer behaviors can be modulated by integrating functional building blocks into a long-range ordered covalent framework 16 – 18 .…”

Hydrogen Bond Organic Frameworks as a Novel Electrochemiluminescence Luminophore: Simple Synthesis and Ultrasensitive Biosensing

“…18 Inspired by this, a series of ECL organic emitters were developed by regulating the aggregation states and networklike assembly. 19 By contrast, many commonly N-rich heterocyclic complexes such as 2,4-diaminotriazinyl (DAT) 20 hold great promise for electrochemical and luminescence applications, owing to their intrinsic advantages of low cost and easy preparation as well as more lone-pair electrons. 21 Meanwhile, the N-rich groups offer extensive units for self-assembly of such aggregation and block the nonradioactive decay of luminogens.…”

“…In the AIE mechanism, such organic molecules show weak fluorescence (FL) in an aqueous states but emit strong FL signals in the aggregated cases . Inspired by this, a series of ECL organic emitters were developed by regulating the aggregation states and network-like assembly …”

Porous organic polymers as a platform for sensing applications

“…Very recently, Yuan and Xiao et al used the sp 2 carbon based COF nanosheet (Py-sp 2 c-CON) to fabricate an electrochemiluminescence (ECL) biosensor. 201 The ultrathin structure of Py-sp 2 c-CON could efficiently shorten the transport distances of electrons, ions and S 2 O 8 2À (co-reactant). Upon introducing /Bu 4 NPF 6 system showed high ECL emission.…”