Elastocapillary flow driven lab-on-a-membrane device based on differential wetting and sedimentation effect for blood plasma separation

We report an elastocapillary flow-driven lab on a membrane device based on differential wetting and sedimentation effect for the separation of plasma from whole blood. Interaction between a thin polydimethylsiloxane (PDMS) membrane (thickness similar to 35 mu m) bonded to the edge of a PDMS substrate and a sample blood drop (of volume similar to 70 mu l) gives rise to deformation of the soft membrane due to the capillary forces providing a conduit and consequent elastocapillary flow of blood. The surface of the PDMS membrane is hydrophilic up to a certain length along the flow direction to support the elastocapillary flow and hydrophobic thereafter to impede the flow. In the hydrophobic region, owing to a much smaller sedimentation time scale (similar to 100 s) as compared to the capillary flow time scale (similar to 1000 s), sedimentation of blood cells occurs thus facilitating separation of plasma from the blood cells in the hydrophobic region. The role of differential wetting and sedimentation effects on the blood plasma separation is studied. The effects of membrane width and thickness, length of the hydrophilic region, erythrocyte sedimentation rate (ESR) on the separation of plasma were investigated. Using a membrane of width 3 mm, thickness 35 mu m, total length 25 mm and hydrophilic length of 4 mm and 70 mu l of whole blood with ESR varying in the range 4 mm h(-1) to 40 mm h(-1), the volume of plasma was in the range of 7.5 mu l to 20 mu l, respectively, which corresponds to a plasma recovery of 22%-49%, respectively. Purity of the plasma from the proposed device was compared with that obtained from centrifugation which showed a good match. The device was integrated with a commercially available detection strip to detect the level of glucose present in the plasma from blood samples of healthy and diabetic patients which are in qualitative agreement with that obtained from conventional tests.