Cu²⁺@NMOFs-to-bimetallic CuFe PBA transformation: An instant catalyst with oxidase-mimicking activity for highly...

In this work, a facile impedance biosensor was constructed for sensitive assaying of miRNA-10b based on the Cu²⁺ modified NH₂-metal organic frameworks (NMOF@Cu²⁺) coupling with a three-dimensional (3D) DNA walker signal amplification strategy. Specifically, abundant Cu²⁺ can adhere to the MOF via the coordination reaction between NH₂ and Cu²⁺, which can be applied as a skeleton to produce CuFe Prussian blue analogue@NMOF (CuFe PBA@NMOF) just in time. Meanwhile, the carboxyl group, which is rich in the organic ligands of the NMOF, can be used to assemble DNA strands (complementary strand, CS) (CS-NMOF@Cu²⁺) for biorecognition reaction. With the introduction of the target, a 3D DNA walker was triggered to shear out large amounts of assistant strands (AS), which were then anchored on the surface of GCE. Afterward, CS-NMOF@Cu²⁺ can be assembled on the GCE by hybridization with AS. Eventually, abundant CuFe PBA@NMOF were generated in situ on the electrode with the help of K₃[Fe(CN)₆], which can catalyze the 4-chloro-1-naphthol (4-CN) precipitation without H₂O₂, thereby increasing the resistance of the platform. Under the optimal conditions, the EIS biosensor presents reliable analytical performance in a wide linear range from 0.8 pM to 250 pM with a low detection limit of 0.5 pM.