Modeling Non Equilibrium Potentiometry to Understand and Control Selectivity and Detection Limit

The majority of present theoretical interpretations of ion-sensor response focus on phase boundary potentials. They assume electroneutrality and equilibrium or steady-state, thus ignoring electrochemical migration and time-dependent effects, respectively. These theoretical approaches, owing to their idealizations, make theorizing on ion distributions and electrical potentials in space and time domains impossible. Moreover, they are in conflict with recent 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.For the above reasons, the Nernst-Planck-Poisson (NPP) equations are employed here to model the non-equilibrium response in a mathematically congruent manner. In the NPP model, electroneutrality and steady-state/equilibrium assumptions are abandoned. Consequently, directly predicting and visualizing the selectivity and the low detection limit variability over time, as well as the influence of other parameters, i.e. ion diffusibility, membrane thickness and permittivity, and primary to interfering ion concentration ratios on ion-sensor responses, are possible. Additionally, the NPP allows for solving the inverse problem i.e. searching for optimal 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 clinical measurements and bioassays are derived

Breakthrough in Modeling of Electrodiffusion Processes; Continuation and Extensions of the Classical Work of Richard Buck

In 1978 Brumleve and Buck published an important paper [1] pertaining to numerical modeling of electrodiffusion. At the time their approach was not immediately recognized and followed. However, it has changed since the beginning of 21st century. The approach of Brumleve and Buck based on Nernst-Planck-Poisson (NPP) equations is utilized to model transient behavior of various electrochemical processes. Multi-layers and reactions allow extending applications to selectivity and low detection limit with time variability, influence of parameters (ion diffusivities, membrane thickness, permittivity, rate constants), and ion interference on ion-sensor responses. Solution of NPP inverse problem allows for optimizing sensor properties and measurement environment. Conditions under which experimentally measured selectivity coefficients are true (unbiased) and detection limit is optimized are demonstrated. Impedance spectra obtained directly from NPPs are presented. Modeling durability and diagnosis of reinforced concrete is presented. Chlorides transport in concrete is modeled using NPPs and compared to other solutions