Rapid optically based measurements of diameter and length for spherical or rod-shaped bacteria in vivo.

The application in light scattering of the Mueller matrix ratio (S34)/(S11) for determining average particle size is extended to a large size parameter range for spherical or randomly oriented rod-shaped particles such as micro-organisms. It is shown that combining the graph of this ratio with a Coulter counter measurement of particle volume gives results in agreement with microscopic measurements. Thus this combination provides a method to measure particle diameter and width simultaneously in real time for elongated particles such as bacteria, which are measured in vivo with this method. An approximate empirical formula is developed to estimate the motion of the extrema in the graph of the oscillating matrix ratio as size changes occur. This formula is also shown to be consistent with wavelength changes.