Ni/Fe‐MOF Electrochemical Transistor Biosensors with 3D Debye Space for Ultrasensitive Detection of Coronavirus Nucleocapsid Protein

Electrochemical transistor (ECT) biosensors can achieve ultrahigh sensitivity, while keeping challenges for large biomolecules due to their sizes over the thickness of the electric double layer (EDL) causing a failure of sensing reaction. Here, wafer-level Ni/Fe-metal-organic framework (MOF) films and corresponding ECT biosensors are fabricated for the detection of coronavirus nucleocapsid protein, which realize an ultralow detection limit of 1 fg mL^-1 and a wide detection range of 1 fg mL^-1 to 100 pg mL^-1. A 3D Debye space, originating from the unique stacking structure of nanosheets and nanoparticles in Ni/Fe-MOF film, is proposed to explain such ultrahigh sensitivity, which ensures the immune-binding and sensing process of the nucleocapsid protein large molecules located in the effective EDL space. Moreover, an appropriate Ni/Fe molar ratio is optimized to enhance the transmission of carriers, thus improving the signal-to-noise ratio and the sensing response. The Ni/Fe-MOF-ECT biosensors will find applications in highly sensitive detection for large biomolecules, and the 3D Debye space may be a design model for constructing other biosensors.