Chapter 2: Theory of Operation 49
Hydrodynamic Focusing
In the flow cell, pressurized sheath fluid surrounds the sample fluid to
hydrodynamically focus the core stream of suspended cells into the center of the
cuvette, where the particles are intercepted by the laser beam.
The difference in pressure between the sheath fluid and the sample fluid can be
used to vary the diameter of the sample core. A lower difference results in a relatively
narrow core stream, while a higher difference results in a wider sample stream.
Ideally, you want the core stream at its minimum diameter so that cells pass
through the laser beam in a single-file stream. However, depending on your
application, a lower resolution might be acceptable in order to acquire the data
more quickly. For example, a higher flow rate is generally used for qualitative
measurements such as immunophenotyping—the data is less resolved but is
acquired more quickly. A lower flow rate is generally used in applications where
greater resolution is critical.
sample flow
sheath flow
laser beams
sheath flow
sample flow
sheath flow
laser beams
sheath flow
low flow rate high flow rate
To Next Page
Loading...
