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Separation in a plug
Separation in a plug
A simple technique was developed to separate plasma in a flowing blood plug. The development of this technique was initially inspired by a unique observation of larger polystyrene beads (>10 µm) or leukemia cells tending to accumulate at the rear of a long moving plug.
Plug to drop
Plug to drop
The separation of plasma from blood cells follows the same rule where the heavier cells flow slower than plasma because of their sedimentation to the bottom of the tubing. As a result, blood cells are collected and aggregated at the end of the plug while the lighter plasma leads the flow in the front. The top picture shows the plasma separation in a 1-uL flowing blood plug (5x dilution of 200-nL finger pricked whole blood) carried by mineral oil; and the plug is then fragmented into nL-droplets for running a cholesterol test in blood.
Pros & Cons:
No microfabrication required to separate plasma from blood
Low cost of disposable tubing: < $0.1
Low blood volume consumption: nL-scale
Low shear rate: ~1 s-1, expected to be lysis-free
Separation efficiency: ~60% for diluted blood in ~5 min
Easy to operate
Easy to couple with droplet-based technology to confine the diffusible signals
Low flow rate/throughput: ~1 μL min-1, enough for POCT
More suitable for diagnostic assays that can accommodate blood dilution
Separation from whole blood takes longer time: ~40 min
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