A New Method to Enhance Electrochemiluminescence of Imine-Based Covalent Organic Frameworks

The application of imine-linked covalent organic frameworks (COFs) in electrochemiluminescence (ECL) is hindered due to their high polarity and instability. At present, there is no effective method to overcome this issue. Herein, a novel quinoline-linked COF, i.e., TAPPDTA0, was synthesized using 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (TAPP) and 2,5-dihydroxyterephthalaldehyde (DTA) as building blocks through a Schiff base reaction with postmodification with the Povarov reaction. The intramolecular hydrogen bond and the quinoline ring stabilize the C═N bond, endowing TAPPDTA0 with excellent ECL performance by suppressing molecular self-rotation and enhancing π-electron delocalization. When TAPPDTA0 works as the luminophore, an "on-off-on" ECL biosensor with Exo III-assisted target recycling amplification strategy showed a remarkably low detection limit (LOD) of 1.67 fM (S/N = 3) toward miRNA-141 assay in a broad linear response from 1 μM to 10 fM. This work opens a new chapter in the design of novel ECL emitters using postmodified imine-linked COFs and expands the application of imine-linked COFs in ECL biosensors.