A glance into the bulk of solvent polymeric pH membranes*

The pH-sensitive chromoionophores brought the dream of the ion-selective membrane scientist close to realization. With the help of these molecules, one can build pH-sensitive, ion-selective electrodes and look into the bulk of solvent polymeric membranes during potentiometric measurements (spectropotentiometry) and image concentration profiles in situ with high spatial and temporal resolution. The combination of electrochemical and optical information helped to interpret non-idealities in the potentiometric responses, suppress or tailor the undesirable transport across sensor membranes, and estimate the residual lifetime of chronically implanted sensors. These novel opportunities provide feedback in membrane optimizations and are expected to lead to sensor systems with picomolar detection limits and superb selectivities.