Addressing the challenge of solution gating in biosensors based on field-effect transistors

Abstract

Transistor-based biosensing (BioFET) is a long-enduring vision for next generation medical diagnostics. The study addresses a challenge associated with the BioFET solution gating. The standard BioFET sensing measurement involves sweeping of the solution gate (Vsol) with a concurrent measurement of the source-drain current (IDS). This IDS-Vsol sweep poses a great challenge, as Vsol does not only determine IDS, but also determines the pH levels, ion concentrations, and electric fields at the sensing area double layer accommodating the biomolecules. Therefore, inevitably, an IDS-Vsol sweep implies that the sensing area double layer is not in an electrochemical equilibrium, but rather in a continuous transient state as electrochemical potential gradients induce transient ion currents continuously affecting double layer hosting the biomolecules and the biological interactions. This challenge calls for a BioFET design which permits IDS sweeping from an off-state to an on-state while keeping Vsol constant and the double layer sensing area in electrochemical equilibrium. The study explores a BioFET design addressing this challenge by decoupling the solution potential from IDS gating. Specific and label-free sensing of ferritin in 0.5 μL drops of 1:100 diluted plasma is pursued. We show an excellent sensing performance once the solution potential and IDS gating are decoupled, with a limit-of-detection of 10 fg/ml, a dynamic range of 10 orders of magnitude in ferritin concentration and excellent linearity and sensitivity. In contrast, a poor sensing performance is recorded for the conventional Vsol sweep performed in parallel to the above. Extensive control measurements quantifying the non-specific signals are reported.