Light scattering measurement in an arc lamp‐based flow cytometer

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Abstract
The epi‐illumination optics employed in most arc lamp‐based flow cytometers may be modified so as to produce a dark‐field configuration which facilitates highly sensitive detection of both forward and large angle light scattering in an instrument with a “jet on open surface” flow chamber. Forward scattering is detected at angles upwards from about 2°, while large angle scattering includes angles above 18°. Theoretical considerations suggest that large angle scattering measured around 20° may be as efficient as that measured at 90° for the purpose of distinguishing cells on the basis of intracellular structure. This was supported by the finding that dual parameter light scattering histograms of leukocyte suspensions obtained with the arc lampbased instrument were closely similar to such histograms recorded with a laserbased instrument with the large angle detector at 90°. Different species of bacteria could be distinguished by means of the dual parameter light scattering device, as could different species of sea algae. The sensitivity of the device is sufficient to measure 0.2 μm polystyrene particles in both forward and large angle scattering.