3D Impedimetric Microfluidic Membrane-Mimic Cassette (IM3) with Interdigitated Electrodes for Fouling Analysis at Membrane Interfaces

Membrane fouling remains a major challenge in water treatment, biomedical, and pharmaceutical fields, yet understanding its mechanisms at the membrane interface remains difficult. Herein, we report a 3D impedimetric microfluidic membrane-mimic (IM3) cassette that integrates a porous membrane between microfluidic channels for real-time fouling investigation via electrochemical impedance spectroscopy (EIS). System validation using fluorescein and KCl electrolytes demonstrated reproducible charge-transfer resistance (Rct) values and confirmed cassette robustness. Colloidal fouling studies using 800 nm polystyrene latex (PS) beads demonstrated a clear concentration-dependent behavior. High particle loading (105 particles/mL) caused rapid, severe impedance increases, indicating extensive pore blockage and cake layer formation. Low loading (101 particles/mL) showed minimal changes, suggesting negligible fouling, as confirmed by scanning electron microscopy. The distribution of relaxation times (DRT) analysis revealed a single dominant relaxation peak at 10–2 s that grew stronger as fouling severity increased, confirming that pore blockage raised interfacial resistance through a unified charge-transfer mechanism rather than caused diffusion-limited processes. A quantitative fouling model using EIS-measured Rct changes captured temporal and concentration dependencies through an exponential growth framework. Maximum fouling extent (Fmax) increased significantly with particle concentration (30% at 101 to 215% at 105 particles/mL), demonstrating concentration-dependent pore blockage. The fouling rate constant (k) showed weak concentration dependence and plateaued at high loadings, indicating the limitation by available deposition sites rather than particle transport. These findings show that for PS beads, fouling is mainly governed by the extent of surface deposition (driven by concentration) rather than by the particle arrival rate (controlled by kinetics). The developed modular IM3 cassette enables customization of different membranes, channel geometries, and flow configurations. These results establish a quantitative framework linking EIS data to physically meaningful fouling phenomena, offering a versatile platform for the mechanistic investigation of dynamic membrane fouling behavior under varying particulate conditions.