Fig. 5: Selecting the most efficient OMIEC for a pOECT-based sensor.

a Top: Transfer curves of the p-type Na⁺-IS-pOECT at [Na⁺] = 0 and 100 mM (as reported in Fig. 3b). The gating voltage is referred to with respect to the electrochemical potential of G_S at different [Na⁺] (vs. G_{S, xM} = 0 M and 100 mM). The double arrow highlights the V_SG distance between the two curves, corresponding to the difference in the OCP of the G_S in the two conditions (ΔOCP). Bottom: transfer curves at different Na⁺ concentrations, back shifted by a ΔV_SG = ΔOCP where the 0 M condition is the reference point. This back shift makes the gating voltage to be referenced with respect to the G_S at 0 M (vs. G_S, _{0 M}). b Transfer curves of the n-type Na⁺-IS-pOECT at different Na⁺ concentrations. The inset reports the transfer curves back shifted by a ΔV_SG = ΔOCP at 0 M Na⁺. c Transfer curves of an n-type and p-type Na⁺-IS-pOECT at [Na⁺] = 0 and 100 mM. The target interactions with the G_S, which causes an increase in the G_S electrochemical potential, lead to a negative shift of the transfer curves. d Normalized I_DS of the n-type Na⁺-IS-pOECT recorded at different Na⁺ concentrations. e Left: Transfer curves of the n-type Cl⁻-IS-pOECT at different Cl⁻ concentrations Right: Calibration curves of the conventional 2-electrode potentiometric setup (ISE) and the pOECT. f Left: Transfer curves of a PEDOT:PSS based Na⁺-IS-pOECT at different Na⁺ concentrations. Right: normalized I_DS of the device.