Hydrogel-Gated MXene-Graphene Field-Effect Transistor for Selective Detection and Screening of SARS-CoV-2 and E. coli Bacteria

Field-effect transistor (FET) biosensors have significantly attracted interest across various disciplines because of their high sensitivity, time-saving, and label-free characteristics. However, it remains a grand challenge to interface the FET biosensor with complex liquid media. Unlike standard liquid electrolytes containing purified protein content, directly exposing FET biosensors to complex biological fluids introduces significant sensing noise, which is caused by the abundance of nonspecific proteins, viruses, and bacteria that adsorb to the biosensor surfaces. In this work, we leverage the hydrogel encapsulation on an MXene–graphene-based FET, which selectively allows the permeation of viruses (e.g., SARS-CoV-2) and bacteria (e.g., E. coli), leading to the high-specificity detection of those biomarkers. The results demonstrated that hydrogel encapsulation could successfully detect the SARS-CoV-2 biomarker at 1 fg/mL while preventing the diffusion of E. coli biomarkers, and the obtained signal output amplitude is twice that of sensors without hydrogel encapsulation, demonstrating significant advantages over conventional bare sensors.