A Comprehensive Study of Faradaic Ion Concentration Polarization for Enhancing Biomolecule Detection

In this study, a bipolar electrode (BPE)-based microfluidic device was constructed to investigate the parameters influencing faradaic ion concentration polarization (fICP). The device comprises two primary components: a main channel and an adjacent buffer channel. Adjusting the gap distance between the main and buffer channels allows simultaneous preconcentration of the solutions branching off from the main channel, increasing the concentration of fluorescent tracer from 0.01 to 25 µg/mL (e.g., 2500-fold) within 100 s. On the other hand, reducing the length of the branch channels decreases the length of the ion depletion zone (IDZ) and enhances the concentration efficiency, with results varying from a 186-fold concentration in the shortest channel (e.g., 22 mm) to a 37-fold concentration in the longest channel (e.g., 57 mm). The study also examined the instability of fICP under high voltage conditions, providing insights for future device design improvements. Finally, the integration of the fICP system with an immuno-biosensor successfully demonstrated an improved limit of detection for the anti-BSA antibody, extending from 10⁻⁸ down to 10⁻¹² g/mL.