Electrochemical microfluidic sensor with sodium ion-imprinted polymer membrane for sensitive and specific detection...

The integration of ion imprinted polymers (IIPs) into microfluidics for rapid and selective detection of salt ions in water is presented. Selective determination of sodium ions without compromising sensitivity is challenging due to the interference from other alkali metals. In this work, a sodium-ion-imprinted polymer (Na-IIP) membrane was synthesized in situ within a microchamber employing 15-Crown-5 (15C5) as ionophore forming ion cavity sites and carboxylic functional groups that act as synthetic receptors for selective interactions with sodium ions. Silver electrodes flanking the membrane enabled electrochemical detection via chronoamperometry. The sensor's performance was assessed across 0-1000 ppm concentration for NaCl, KCl, and KNO₃. It demonstrated NaCl limits of detection and quantification of 58 ppb and 190 ppb, respectively, with a sensitivity of 9.1 nA/ppb. Specificity studies revealed a strong differential sensitivity towards sodium ions, with NaCl response exceeding KCl and KNO₃ responses by 75.1% and 75.5% at 1 ppm, 74.5% and 59.3% at 10 ppm, 60.1%, and 58.4% at 100 ppm, and 129.7% and 146.1% at 1000 ppm, respectively. Selectivity was confirmed in both controlled multi-ion mixtures and spiked tap water, supporting the sensor's compatibility with realistic ionic backgrounds. This work demonstrates the potential of combining ion imprinting with microfluidics to create sensitive and selective sensors for ion detection. Unlike conventional electrode-coated approaches, the use of a standalone IIP membrane enhances reproducibility, simplifies fabrication, and enables direct analyte-membrane interaction. Future applications could extend to detecting multiple analytes, with integration into fully automated Point-of-Need systems for on-site water testing.