Chapter 2: Theory of Operation 63
Figure 2-14 Sorting
Drop Formation
The BD FACSAria cytometer is unique in that drop drive energy is constantly
applied to the stream; droplets form as soon as you turn on the stream. Sample
interrogation takes place upstream of the stream vibration so that analysis is not
affected by the drop drive.
A drop breakoff image is created using an LED strobe and a video camera. The
image is displayed in the Breakoff window. (See Breakoff Window on page 64.)
Patented Sweet Spot technology
*
analyzes the drop breakoff image and provides
feedback to the appropriate cytometer controls.
* US Patent No. 5,700,692
Charge is applied via the stream-charging wire in
the barb.
Sample generates light scatter and fluorescent
signal; signal is analyzed.
The charged droplet breaks off.
Deflection plates attract or repel the charged
droplet.
Uncharged droplets pass to waste.
Charged drops containing particles of interest are
collected.
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