We report an asymmetric capillary-driven PDMS microchannel device with a hydrophobic patch for separation of plasma from sample blood and subsequent detection of glucose. A microchannel of cross-section 1000×400μm, with hydrophilic walls (on three sides) achieved by using oxygen plasma exposure enables capillary flow of blood introduced at the inlet. A hydrophobic patch (on all four sides) of width 1.0cm, located at 10mm from the device inlet, created in the microchannel impedes the flow of blood and the accumulated blood cells at the patch form a self-built-in filter to facilitate separation of plasma. 450nl of plasma was obtained within 15min.