An unexpected signature of Lorenz-Mie scattering observed in flowcytometric experiments

Detailed analysis of elastic light scattering by spheresin FlowCytometers shows unexpected Lorenz-Miescattering patterns. The complete scattering matrix S ofspheres was measured. Two parameter scatterplots withx- and y- coordinates determined by the S11 + Sij andS11 - Sij values were obtained. Samples of sphereswith very narrow size distributions were analyzed andproduced unexpected two parameter scatterplots. Insteadof compact distributions we observed Lissajous-likeloops. Simulation of the scatterplots, using Lorenz-Mietheory, shows that these loops are not due toexperimental errors, but due to true Lorenz-Miescattering. We show that the loops originate from thesensitivity of the scattered field on the radius of thespheres. This work demonstrates that the interpretationof rare events and hidden features in FlowCytometryneeds reconsideration.