INTRODUCTION TO FLOW CYTOMETRY - Flow Cytometry in Drug Discovery and Development - page 4

FIGURE 1.2 Diagrammatic representation of a basic flow cytometer. The fluorescently
labeled cells are hydrodynamically focused into a single file in the flow cell. Individual cells are
excited by the laser light source and the fluorescence emissions, FSC, and SSC are detected. The
cells can then be given a particular charge based on their fluorescence profile and deflected
toward the oppositely charged plates. In the figure, light grey cells and dark grey cells are given
negative and positive charges, respectively, and are thus deflected toward two different tubes.
Scatter or fluorescence is captured, filtered (based on the wavelength), and directed to
the appropriate photodetectors for conversion to electronic signals. The electronics in
the flow cytometer amplify the signal and convert the analog data to digital data,
which can then be analyzed by computer software programs.
1.3 FLUIDICS
1.3.1 Flow Cells
In order to perform flow cytometric analysis, the sample must be in a suspension and
the cell in the sample streammust be centered in the laminar flow [49]. Hydrodynamic
focusing induces cells to orient with their long axis parallel to the flow. The end result
is that the introduced sample passes by the laser with each cell oriented in the center of
the sample stream in a particular manner in three dimensions.