Printed Ion-Selective Electrodes with Silicone

Ion concentrations are critical to a wide-variety of disciplines including precision agriculture and health monitoring. However, for many of these applications continuous measurements are difficult to obtain and require stable, low-power sensors that may be replaced at a low-cost. Solid-contact ion-selective electrodes are potentiometric sensors that operate under near-zero current conditions making them ideal for low-power applications; however, the drift of these sensors over time limits their use for continuous, calibration-free monitoring. Conventional ion-selective electrodes rely on a polyvinyl chloride (PVC) membrane that is susceptible to drift due to water layer formation and leaching of membrane components. Here, alternative membrane compositions, including plasticizer free-silicone membranes, are compared with conventional PVC membranes using printed electrodes. Printed electrode and transducer layers allow for low-cost fabrication and rapid prototyping while commercially available silicones are used to develop silicone ion-selective layers for K⁺ and NO₃^- as well as silicone outer layers. The resulting printed, flexible ion-selective electrodes with silicone layers show preliminary sensitivities greater than 50mV/dec with sensor drift less than 20mV/dec over a 30-day study, which demonstrates an order of magnitude reduction in sensor drift compared to the control PVC membranes. Additional characterization of water layer formation, electrode impedance spectroscopy, and selectivity is carried out to analyze sensor performance. Overall, this work illustrates the feasibility of continuous ion monitoring with low-cost printed ion-selective electrodes utilizing alternative membrane compositions that improve the lifetime and stability.