Supramolecular membrane transport: From biomimics to membrane sensors

A stable, long-lived membrane sensor for dissolved oxygen is reported. A conventional amperometric Clark cell was augmented through the addition of an ion-exchange carrier to the membrane to permit export of hydroxide in exchange for chloride in the sample solution. The choice of a suitable carrier was determined from two types of supramolecular principles: (1) the characteristic flux as a function of the magnitude of the two-phase ion exchange equilibrium constant (K_ex) for an antiport transport cycle as derived for biomimetic ion transport studies and (2) the use of guanidinium ion exchangers to provide hydrogen-bonding in addition to electrostatic recognition for enhanced hydroxide/chloride selectivity. The membrane of the sensor supports the anticipated ion-exchange as it continues to provide stable current beyond the point where the initial internal chloride would be entirely consumed. As a consequence, stable and responsive sensors can be fabricated using planar techniques such as screen printing.