Tuning AC Electrokinetic Flow to Enhance Nanoparticle Accumulation in Low‐Conductivity Solutions

Abstract This study presents a novel AC electrokinetics‐based microfluidic approach for nanoparticle trapping and accumulation in low‐conductive aqueous solutions. The concentration performance is systematically investigated by tuning the applied voltage and frequency, showing that AC electrothermal flow (ACET)‐induced vortex trapping provides a field strength‐dependent concentration enhancement and a high concentration factor. The findings reveal a substantial enhancement in the concentration of polystyrene nanoparticles with sizes of 100 nm. Specifically, a 16‐fold enrichment in the concentration is achieved compared with the initial concentration of the sample. In addition, the effectiveness of a high‐frequency AC voltage (50–150 kHz) versus a low‐frequency accumulation (1–20 kHz) for nanoparticle accumulation is compared and it is determined that at high frequencies, the trapped nanoparticles accumulate at a single area at the electrode gap, which differs from the low‐frequency accumulation observed in previous studies. The complex behavior of nanoparticle accumulation is analyzed, including the differences in the hydrodynamic flow patterns between AC electroosmosis and ACET flow. The proposed technique provides a powerful tool for the efficient and controllable manipulation of nanoparticles and contributes to a highly sensitive characterization of nanomaterials in low‐conductivity liquid samples in microfluidic systems through efficient particle trapping.