Localized Edge-Electrode Field Coupled with Acoustic Focusing Enables High-Sensitivity Impedance Detection in Wide-Channel

Leukocyte analysis constitutes a fundamental pillar in clinical hematology due to the dynamic variations in subpopulation profiles during pathological processes, such as infections and inflammation. While impedance flow cytometry provides a label-free differentiation strategy based on intrinsic electrical properties, it is constrained by position-dependent signal variation and microchannel clogging. To address these limitations, we proposed a monolithically integrated microfluidic device that synergistically combined a bulk acoustic wave (BAW) resonator with coplanar edge electrodes projecting into one side of a wide microchannel. This design strategically concentrates the electric field intensity to a localized region near the electrodes, effectively eliminating clogging risks and enhancing detection sensitivity. Simultaneously, the BAW-induced acoustic streaming enables precise three-dimensional (3D) cell focusing, thereby circumventing the impact of the inherent nonuniform electric field. Additionally, the sheath-free focusing trajectory is flexibly tunable via modifications to the resonator geometry, enabling facile alignment with electrode properties for optimal cell positioning within the sensing zone. This design yielded a 5.04-fold enhancement in detection sensitivity compared to conventional electrode configurations. By characterizing both cell size and internal complexity through multifrequency impedance responses, the system achieved 3-part leukocyte classification comparable to hospital test reports, demonstrating its potential for practical medical and point-of-care testing (POCT) applications.