Sensitive and Selective Electrochemical Detection of Lithium Using a Low-Cost Ion-Imprinted Polymer-Based Microfluidic Sensor

Excessive lithium (Li⁺) discharge into water systems poses environmental and health risks, necessitating accurate and selective monitoring. Most state-of-the-art approaches involve coating receptors onto electrodes, a process that is time-, cost-, and labor-intensive. This study presents a microfluidic electrochemical sensor that integrates a stand-alone, in situ synthesized lithium-ion imprinted polymer (Li-IIP) membrane, eliminating the need for electrode surface pretreatment and receptor-layer bonding. The methacrylic acid (MAA) membrane-based Li-IIP sensor achieved a limit of detection (LoD) of 168 ppb, a limit of quantification (LoQ) of 185 ppb, and a sensitivity of 11.6 nA/ppm, representing a 64.9% reduction in LoD and a 4.6-fold reduction in LoQ compared with the MAA-based nonimprinted polymer (NIP) sensor, and a 6.8-fold and 8.9-fold reduction in LoD and LoQ, respectively, compared with the membrane-less sensor. Specificity studies revealed 35.5% and 138.8% greater response to Li⁺ than Na⁺ and K⁺, respectively, at 20 ppm. Selectivity studies demonstrated 25–74.6% stronger responses in Li-dominant mixtures. Interference tests showed moderate to minimal suppression from competing molecules, i.e., NaCl, KCl, NaNO₃, KNO₃, and Na₂SO₄ at 10 and 20 ppm. Recovery tests in real tap waters yielded 68.5%, 74.3%, and 93.6% for 20, 30, and 40 ppm Li⁺ spikes with less than 5% relative standard deviation (SD). The standalone membrane-based microfluidic design of this sensor has the potential to enable a cost-effective, portable, and scalable solution for real-time Li⁺ monitoring in water quality, environmental surveillance, and lithium extraction applications in the future.