and the liquid and the reference electrode at the other side. The latter term is in fact the reference electrode potential relative to vacuum Eref , which includes ΦM. The interface potential at the gate oxide-electrolyte interface is determined by the surface dipole potential of the solution χsol, which is a constant, and the surface potential ψo, which results from a chemical reaction, usually governed by the dissociation of oxide surface groups. The resulting equation for the flatband voltage of an ISFET is thus given by: