Shear-Mediated Platelet Adhesion Analysis in Less Than 100 μ L of Blood: Toward a POC Platelet Diagnostic

We report a microfluidic chip-based hydrodynamic focusing approach that minimizes sample volume for the analysis of cell-surface interactions under controlled fluid-shear conditions. Assays of statistically meaningful numbers of translocating platelets interacting with immobilized von Willebrand factor at arterial shear rates (~1500 s^-1) are demonstrated. By controlling spatial disposition and relative flow rates of two contacting fluid streams, e.g., sample (blood) and aqueous buffer, on-chip hydrodynamic focusing guides the cell-containing stream across the protein surface as a thin fluid layer, consuming ~50 μL of undiluted whole blood for a 2-min platelet assay. Control of wall shear stress is independent of sample consumption for a given flow time. The device design implements a mass-manufacturable fabrication approach. Fluorescent labeling of cells enables readout using standard microscopy tools. Customized image-analysis software rapidly quantifies cellular surface coverage and aggregate size distributions as a function of time during blood-flow analyses, facilitating assessment of drug treatment efficacy or diagnosis of disease state.