Electrochemical Microfluidic Sensors with Integrated Ion-Selective Polymer Membranes for the Detection of Trace Ions in Water

Abstract

There is an increasing demand for low-cost, portable, and sensitive sensing technologies for detecting trace levels of metal ions in water to support public health, environmental monitoring, and energy applications. Traditional analytical methods, while accurate, are limited by their reliance on bulky equipment, high cost, and complex electrode modification, making them unsuitable for real-time or on-site use. This research addresses these limitations by developing a microfluidic electrochemical sensor platform that integrates in-situ synthesized, stand-alone ion-imprinted polymer (IIP) membranes for the selective detection of sodium (Na⁺), lead (Pb²⁺), and lithium (Li⁺) ions in water. The study employed a stepwise methodology: an ion-selective polymer membrane was first developed to detect salinity, achieving a 28-fold sensitivity improvement and a detection limit of 0.45 ppm. Next, a Na-IIP membrane using 15-crown-5 as an ionophore achieved 58 ppb detection with over threefold sensitivity enhancement. Finally, Pb-IIP and Li-IIP membranes were developed, attaining detection limits of 7.3 ppb and 168 ppb, respectively, with high selectivity over competing ions. All configurations demonstrated high reproducibility, multi-ion selectivity, and recovery rates ranging from 69% to 109% in municipal tap water. The stand-alone membrane design simplifies fabrication, enhances stability, and is compatible with continuous-flow operation. This work advances the development of scalable, point-of-need sensing systems and offers a foundation for future multiplexed and automated water quality monitoring platforms.