Semi-quantitative graphene chemiresistor enzyme immunoassay for simple and sensitive antigen detection

Graphene is an ideal platform for sensing biomolecule charges due to its high electron/hole mobilities and 2D nature. However, when directly detecting biomolecules on graphene surfaces, it is important to consider their charge magnitude and the impact of Debye screening, which limits the detectable biomolecule types. Therefore, we propose a graphene chemiresistor enzyme immunoassay that allows for the detection of all protein types, regardless of charge or size. In this study, we immobilized antibodies on rigid glass surfaces rather than graphene surfaces to simplify the washing process and reduce noise caused by solution flow on graphene. As an example, we used influenza virus nucleoprotein as the antigen and urease as the enzyme. By measuring changes in graphene's electrical conductivity resulting from ammonium ions generated by enzymatic reactions, we confirmed antigen presence. The responsiveness of the graphene chemiresistor varied depending on antigen concentration, successfully detecting 100 pM antigens in this experiment. Our semi-quantitative method offers a simple and highly sensitive electrical detection of antigens.