Abstract: A microfilter utilizing the principles of tangential flow to prevent clogging, and sloped channel sides to overcome surface tension effects is provided which has feed inlet and exit connected by a feed flow channel; a barrier channel parallel to the feed flow channel, and a filtrate collection channel parallel to the barrier channel so that liquid can flow from the feed flow channel through the barrier channel which is too small to accommodate the particles, into the filtrate collection channel, and from then through a filtrate flow channel to a filtrate exit. Several picoliters of cell-free plasma are recovered from one drop of blood for analysis.