Abstract
In most interpretations of ion-sensor response phase boundary potentials are used. They assume electroneutrality and equilibrium or steady-state, thus ignore electrochemical migration and time-dependent effects. It is in conflict with many experimental reports on ion-sensors, in which both kinetic (time-dependent) discrimination of ions to improve selectivity, and non-equilibrium transmembrane ion-transport for lowering detection limits, are deliberately used. The Nernst-Planck-Poisson (NPP) equations are used to model the non-equilibrium response. In the NPP model, electroneutrality and steady-state/equilibrium assumptions are abandoned and directly predicting the selectivity and the low detection limit variability over time, and the influence of other parameters, e.g. ion diffusibility, are possible. The NPP allows for solving the inverse problem i.e. to optimize sensor properties and measurement conditions via target functions and hierarchical modeling. The conditions under which experimentally measured selectivity coefficients are true (unbiased) and detection limits are optimized are demonstrated, and practical conclusions relevant to bioassays are derived.
Published Version
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