Although the COPAS Biosort instrument is designed on the basic principles of flow cytometry, it differs from those of traditional flow cytometers optimized for high-speed cell analysis and sorting in two important areas to permit larger objects to be analyzed:
1. The large-bore fluidics and flow cell design permits handling objects as wide as 150-200
2. The heart of the COPAS technology is a gentle pneumatic sorting mechanism located after the flow cell that does not harm or change objects, and is, therefore, safe even for the collection of live biological materials or sensitive chemistries.
A constant stream of the worm sample is allowed to flow from a continuously mixing sample cup to a preanalysis chamber, where it is surrounded by a "sheath" solution to produce a stabilized laminar flow. The laminar flow acts to focus the animals to the center of the flow stream and to orient them lengthwise, in the direction of the flow. Animals then pass into the flow cell, where they are illuminated by two low-energy lasers. A red diode laser (670 nm) measures the axial length and the optical density of the object, and a multiline laser is used to excite any fluorophores present. Based on the measured optical parameters (size, optical density, and fluorescence) the operator can then set gated regions for sorting and collecting the population of interest into multiwell microtiter plates or stationary receptacles (Fig. 2).
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