'WO 021'33163
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`PCTIUSOIJZ-‘jfié?
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`-37-
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`will contain two or more molecules, cells or vii-ions. This is to ensure that for the large
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`majority of measurements, the level of reporter measured in each droplet as it passes
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`through the detection region corresponds to a single nioleoule, cell or virion and not to
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`two or more molecules, cells or virions.
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`The parameters which govern this relationship are the volume ofthe droplets and
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`the concentration of molecules, cells or virions in the sample solution. The probability
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`that a droplet will contain two or more molecules cells or Virions {Pa} can be expressed
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`as
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`S 2 = 1" {1+ [Virion] s V} x e
`P
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`~[Iai1ion1xl’
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`where "[t-irion]fl is the concentration of molecules, cells or Vitions in units of number of
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`molecules, cells or virions per cubic micron turf), and Via the volume of the droplet in
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`units of unia.
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`It will be appreciated that P52 can be minimized by decreasing the concentration
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`of molecules, cells or virions in the sample solution. However, decreasing the
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`concentration of molecules, cells or Virions in the sample solution also results in an
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`increased volume of solution processed through the device and can result in longer run
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`times. Accordingly, it is desirable to minimize to presence of multiple molecules, cells
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`or Virions in the droplets (thereby increasing the accuracy of the sorting) and to reduce
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`the volume of sample, thereby pennitting a sorted sample in a reasonable time in a
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`reasonable volume containing an acceptable concentration ofmolecules, cells or Virions.
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`The maximum tolerable P52 depends on the desired "purity" ofthe sorted sample.
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`The "purity" in this case refers to the fraction of sorted molecules, cells or virions that
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`posses a desired characteristic (eg, display a particular antigen, are in a specified size
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`range or are a partieular type ofmolecule, cell or vii-ion). The purity ofthe sorted sample
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`is inversely proportional to Pig. For example, in applications where high purity is not
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`needed or desired a relatively high P5,, (age, Page 0.2.) may be acceptable. For most
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`applications, maintaining P,2 at or below about 0.1, preferably at or below about 0.01,
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`provides satisfactory results.
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`A sample solution containing amixture or population ofmolecule, sells or VlI‘lQI‘lS‘
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`in a suitable carrier fluid (such as a liquid or butter described above) is supplied to the
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`sample inlet region, and droplets of the sample solution are introduced, at the droplet
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`id]
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`10
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`15
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`is») U:
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`30
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