Low-level salinity monitoring in drinking water using an electrochemical microfluidic sensor with an ion-selective polymer membrane

Sensitive methods for detecting low salt levels (<100 ppm) in drinking water are limited. Current techniques lack specificity or are too costly and complex for point-of-need use. This study presents an innovative electrochemical sensor for precise monitoring of low-level salt ions in drinking water. It integrates an in-situ prepared, UV-curable standalone Ion-Selective Polymer (ISP) membrane within a Polymethyl methacrylate-based microfluidic chip. The ISP membrane containing carboxylic and amide functional groups selectively interacts with target ions. This interaction alters the electrochemical signal, which is measured using two electrodes prepared on either side of the ISP membrane. Chronoamperometry was used to assess the sensor's performance in the presence of different salt ions (i.e., NaCl, KCl, NaNO 3 , and KNO 3 ) from 0 to 800 ppm concentrations. The ISP membrane exhibited significantly higher selectivity towards Na + ions. When compared with a membrane-less sensor, the ISP membrane-integrated device showcased a 87 % improvement in the limit of detection from 3.39 to 0.45 ppm, an 91.6 % reduction in the limit of quantification from 5.84 to 0.49 ppm, and a 28.7-fold increase in sensitivity from 0.7 to 20.1 nA/ppm. Furthermore, the sensor was validated using diluted municipal tap water, achieving recoveries between 84.7 % and 105 % with RSDs below 10 %. The ISP membrane composition can be tailor-made for a wide range of biological and chemical contaminants while the microfluidic chip design is suitable for scalable manufacturing and integration into Point-of-Need testing platforms. • Developed a low-cost electrochemical microfluidic sensor for low-limit salinity monitoring. • UV-curable, in-situ synthesized stand-alone ISP membrane enhances sensor performance. • Demonstrates high sensitivity and specificity for Na + and K + ions at trace levels. • Validates Na + sensitivity in duplex and multiplex salt mixtures. • Cost-effective, adaptable polymer platform with potential for selective contaminant detection.