SOFT X-RAY TRANSPARENT FLOW CELL FOR WATER WINDOW MICROSCOPY WITH INTEGRATED DIELECTROPHORETIC CELL HANDLING

Abstract

Soft X-ray (SXR) microscopy in the water window (284 eV – 543 eV) is a powerful technique enabling label-free whole-cell imaging with an intrinsic structural contrast. Studying living cells in their native aqueous environment, rather than cryopreserved specimens, allows direct, time-resolved observation of biological processes and yields physiologically relevant insights. However, imaging hydrated biological specimens under the vacuum conditions required for SXR microscopy remains challenging, requiring sample environments that simultaneously provide liquid confinement, vacuum compatibility, stable cell positioning, and efficient sample handling. Existing SXR-transparent flow cells often rely on artificial adhesion or fixation, limiting active manipulation, and efficient turnover. Here, we present a vacuum-compatible microfluidic flow cell for water-window SXR microscopy with integrated dielectrophoretic (DEP) cell and particle handling. The device combines X-ray-transparent silicon nitride (Si₃N₄) membranes, microfluidic sample exchange, and DEP-based trapping of suspended cells within a thin liquid layer. Unlike conventional static sample holders, the platform allows fluidic replacement of samples without venting the microscope and enables controlled handling of individual suspended cells in their native aqueous environment. Using polystyrene particles and Jurkat cells, we characterized the DEP trapping performance and demonstrate stable confinement within the microfluidic channel. Integrated with a laboratory-based water-window SXR microscope, the platform enables imaging of dielectrophoretically trapped algal cells from different species in liquid during a single days-long vacuum session. These results establish the feasibility of combining DEP-based cell handling, microfluidic sample exchange, and water-window SXR microscopy in a single experimental platform and provide a foundation for future studies requiring controlled manipulation of hydrated cells during SXR imaging.