Quasi-elastic light scattering from large anisotropic particles: application to the red blood cells

The usefulness of dynamic light scattering measurements for the determinati on of particle size and shape in suspensions of biological objects is well established. However, when the particle sizes are larger than the wavelengt h of the incident light, so that structural information on the scattering p articles can be made available, the analysis of the correlation function of the scattered light requires a careful examination, owing to the problem i nvolved in its theoretical description. In this note, dynamic light scattering techniques were employed for the det ermination of the size of human normal erythrocytes in physiological saline solution (isotonic solution) with the aim to discuss in detail the differe nt effects that contribute to the scattered light intensity distribution an d to evidentiate how correct information can be made available only when th e anisotropic contribution to the translational diffusion coefficient of th e erythrocyte cells is properly taken into account. In the case of erythroc ytes, this effect produces deviation of the order of 8-10% in the evaluatio n of the cell size (the cell diameter and cell thickness) that can be accou nted for by an appropriate dependence upon time of the autocorrelation func tion. Once the electric field autocorrelation function, where the intrapart icle correlation function contains the correction for the anisotropic contr ibution, is considered, reasonable agreement was obtained between the data deduced from light scattering methods and those from scanning electron micr oscope pictures. (C) 2000 Elsevier Science S.A. All rights reserved.