Light-scattering properties of individual erythrocytes

We have studied the light-scattering properties of human erythrocytes both experimentally and theoretically. In the experimental study measurements we re performed with a Scanning Flow Cytometer (SFC). The SFC can measure the light-scattering pattern (indicatrix) of an individual particle over an ang ular range of 10-60 degrees. We have observed polymorphism in the measured set of indicatrices. To understand the reason for this polymorphism, we hav e made a theoretical study of the scattering properties of erythrocytes. Th e Wentzei-Kramer-Brillouin approximation has been employed to calculate ind icatrices of individual erythrocytes in different orientations relative to the incident light beam. The indicatrices were calculated over an angular r ange of 15-35 degrees. A comparison of the experimentally measured and theo retically calculated indicatrices shows that the polymorphism is due mainly to the different orientation of the erythrocytes in the flow. The effect c aused by the Poiseuille profile of the how on an individual erythrocyte wit hin the SFC cuvette capillary was studied theoretically by use of the Stoke s approximation. Rotation of an erythrocyte was predicted by this theoretic al analysis, and this prediction was further verified by comparison with ex perimental results. (C) 1999 Optical Society of America.