Sensing regimes in potentiometric immunoassays

Potentiometric immunoassays, largely based on field-effect-transistor (FET) technologies, have demonstrated exceptional performance, achieving limits of detection (LODs) in the 10–100 zeptomolar range — surpassing established methods such as ELISA-based assays. However, despite more than three decades of research, no immuno-FET technology has yet reached commercial implementation. This Perspective critically examines studies on immuno-FETs across organic, inorganic and 2D-material platforms, focusing on devices with a millimetre-scale detection interface, either metallic (gate electrode) or semiconducting (channel material), biofunctionalized with trillions of capturing antibodies. Two distinct sensing regimes can be identified: a double-layer regime, effective at nanomolar antigen concentrations; and a pH-shift (ΔpH)-enabled regime, which allows detection of a single molecule or a few molecules in a droplet. In both regimes, the threshold voltage shifts proportionally to the logarithm of antigen concentration. However, owing to the non-conducting electronic–ionic interface, the system deviates from Nernstian behaviour, making quantification challenging. The double-layer regime relies on antigen mass stacking on top of the capturing layer, whereas the ΔpH-enabled regime features an amplification within the capturing 2D layer, where pH conditioning enables ultralow LODs. In this regime, immuno-FETs are competitive for qualitative, single-molecule point-of-care diagnostics. Controlling the capturing interface and understanding the biochemical amplification effects underpinning the ΔpH-enabled regime is essential for improving the reliability of FET-based immunoassays.