205
polarizer and into a detector labeled depolarized light orthogonal light scatter. The
discrimination among the cell types is apparent on a bivariate dot plot. This measurement is
roughly equivalent to sensing the scattering matrix element S12. For a very small
homogeneous particle passing through a flow cytometer with a vertical linearly polarized laser
beam, the light scattered at right angles remains vertically polarized. For a larger particle or
one with significant internal structure, some of the vertically polarized light is converted into
horizontally polarized light.
A method for making scattering matrix element measurements in a flow cytometer has been
presented (Sloot et al. 1989). The investigators show an optical configuration for making the
measurements and develop the theory to take into account the tightly focused laser beam and
the use of large area scattered light detectors. Van De Merwe et al. (1989) measured
scattering angular distributions of S34/Sll for cuvette suspensions of E. coli bacteria. They
showed that the measurements were strongly correlated to bacterial size. They tested the
sensitivity of this measurement to changes in internal structure by inducing virus production
in the bacteria. S34/SlI did not change until the bacteria were lysed by the virus growth
process. These discouraging results for cuvette suspensions do not invalidate the use of the
technique for single particles in flow. It is clear, however, that a great deal of care must be
taken when making such measurements and in interpreting the results in terms of cell
structure.
This depolarization phenomenon has been exploited by another group of investigators to
distinguish several groups of eukaryotic marine phytoplankton (Olson et al. 1989). Separate
photodiode detectors were placed above and below the center of the laser beam to intercept
scattered light between 10 degrees and 19 degrees. This is apparently far enough from the
forward direction for polarization differences to be observable. The upper detector was
covered with a vertically oriented polarizer and the lower detector was covered with a
horizontally oriented polarizer. Coccolith-covered cells were readily distinguished from ~laked
cells and loose Coccoliths of the coccolithophorid H. carterae.
polarizer and into a detector labeled depolarized light orthogonal light scatter. The
discrimination among the cell types is apparent on a bivariate dot plot. This measurement is
roughly equivalent to sensing the scattering matrix element S12. For a very small
homogeneous particle passing through a flow cytometer with a vertical linearly polarized laser
beam, the light scattered at right angles remains vertically polarized. For a larger particle or
one with significant internal structure, some of the vertically polarized light is converted into
horizontally polarized light.
A method for making scattering matrix element measurements in a flow cytometer has been
presented (Sloot et al. 1989). The investigators show an optical configuration for making the
measurements and develop the theory to take into account the tightly focused laser beam and
the use of large area scattered light detectors. Van De Merwe et al. (1989) measured
scattering angular distributions of S34/Sll for cuvette suspensions of E. coli bacteria. They
showed that the measurements were strongly correlated to bacterial size. They tested the
sensitivity of this measurement to changes in internal structure by inducing virus production
in the bacteria. S34/SlI did not change until the bacteria were lysed by the virus growth
process. These discouraging results for cuvette suspensions do not invalidate the use of the
technique for single particles in flow. It is clear, however, that a great deal of care must be
taken when making such measurements and in interpreting the results in terms of cell
structure.
This depolarization phenomenon has been exploited by another group of investigators to
distinguish several groups of eukaryotic marine phytoplankton (Olson et al. 1989). Separate
photodiode detectors were placed above and below the center of the laser beam to intercept
scattered light between 10 degrees and 19 degrees. This is apparently far enough from the
forward direction for polarization differences to be observable. The upper detector was
covered with a vertically oriented polarizer and the lower detector was covered with a
horizontally oriented polarizer. Coccolith-covered cells were readily distinguished from ~laked
cells and loose Coccoliths of the coccolithophorid H. carterae.