Electrohydrodynamic Vortex Imaging: A New Tool for Understanding Mass Transfer in Surface-Based Biosensors

Surface-based biosensor performance is generally limited by mass transfer, especially when detecting low-concentrated species. To address this, dielectrophoresis (DEP) and alternating current electroosmosis (ACEO) can be combined to enhance mass transfer, increasing the target concentration near the sensor. This article presents a method for real-time direct imaging of electrohydrodynamic (EHD) effects on a microparticle suspension within a microfluidic chamber enclosed by two opposing electrodes. This top-bottom configuration was poorly studied in the literature for ACEO. The system presented thereby allows measurements of fluid flow profiles perpendicular to the electrode surface. The velocity of fluorescent latex microsphere tracers was measured as a function of signal frequency, potential, and electrolyte conductivity. This setup enables direct observation of vortices and particle-depleted areas, offering a valuable tool for selecting optimal input parameters-such as electric field, conductivity, and electrode dimensions-to efficiently concentrate microparticles near the sensor. Additionally, a numerical model developed in COMSOL and adapted for this top-bottom configuration enhances understanding of key parameters influencing EHD phenomena.