Development of a 3D-Membrane-Integrated Microfluidic System for Electrochemical Characterization of Membrane

Understanding interfacial interactions on porous water filtration membranes and developing innovative methods to reduce membrane fouling remain key challenges in membrane-based water treatment systems. This work presents an innovative 3D microfluidic system that integrates electrochemical impedance spectroscopy (EIS) to examine membrane-electrolyte interactions on nonconductive polymeric membranes. Glass slides patterned with micro-gold electrodes act as the working, reference, and counter electrodes. In contrast, a porous nylon membrane is sandwiched between them using pressure-sensitive double-sided tape with microchannels. The device was tested through colorimetric and fluorescence-based leakage analysis, confirming complete fluid confinement within the microchannel and demonstrating that the tape-membrane interfaces are robust and leak-free. To assess the electrochemical performance of the platform, EIS was performed at varying KCl concentrations as the electrolyte. The results showed a strong link between charge transfer resistance and electrolyte ionic strength, in line with classical electrochemical theory, which states that higher ionic strength compresses the electric double layer and promotes faster charge transfer. As KCl concentration increased from 1 to 10 and 100 mM, the charge transfer resistance decreased significantly, indicating improved ionic conductivity and lower interfacial impedance, and producing stable, reproducible Nyquist spectra at higher concentrations. Comparison with the control configuration (without the membrane) revealed consistently higher charge-transfer resistance in the membrane-integrated device, confirming the porous membrane's contribution to ion-transport resistance. Overall, these findings demonstrate that the microfluidic membrane device offers a leak-free, stable, and precisely controlled microscale environment, ideal for studying interfacial electrochemical processes and fouling behavior. It also provides a versatile foundation for future integration of spectroscopic, photoelectrochemical, and advanced membrane-science techniques for real-time mechanistic investigations.