Ionophore-based ion optodes without a reference ion: electrogenerated chemiluminescence for potentiometric sensors

We report here on an electrogenerated chemiluminescence (ECL) readout for potentiometric ion-sensors, thereby offering an optical sensor output without the need for a reference ion (typically the hydrogen ion) that inconveniences ionophore based optical sensor principles. The compartment for ECL generation is physically separated from the sample by a bridge, and no current flows through the sample compartment. Here, three different types of ion selective membranes (Ca2+, Na+ and K+) are read-out individually and sequentially with this methodology. The repeatabilities are found as 0.5 to 1% of integrated light output, which translates into a relative uncertainty in the activity measurement of about 10%. This uncertainty appears to originate primarily at the ECL generating gold electrode, not at the potentiometric sensor. Other analytical figures of merit such as measuring range, sensitivity, optimal applied potential for ECL generation, and ion selectivity are also described.