Figure 1.

Contrasting blood circulation inside the body with artificially created structures used to realize hydrodynamic focusing in single-cell analysis. (A) The heart pumps oxygen-rich blood from its left chamber into the circulatory system. Blood flows through arteries and arterioles before it reaches capillaries supplying target organs and cells with nutrients and oxygen. Subsequently, oxygen-poor blood continues through venules and veins back into the right chamber of the heart. From there, it is pumped to the lungs, where red blood cells are replenished with oxygen. The blood finally flows back into the left heart chamber, from where it can re-enter the circulatory system. (B) Hydrodynamic focusing in flow cytometry. A sheath fluid flow within a capillary engulfs a central cell-laden stream. Control of the velocities and/or densities of the two liquid streams allows formation of a stable two-layer flow, with cells moving in single file toward a detector and outlet nozzle.