Localized light absorption by hemoglobins of an erythrocyte suspension

A correction factor accounting for the differences between the absorption spectra of an erythrocyte suspension and hemolyzed blood (hemoglobin solution) has been calculated. Erythrocytes and their aggregates are simulated by “soft” cylindrical (disk-shaped) particles. The anomalous diffraction approximation is used. At equal absorbing mass, the absorption coefficient of the suspension in the blue spectral region is shown to be capable of being several times lower than that of the solution due to localization of the absorber in erythrocytes. The hemoglobin localization effect is less important for λ _em > 600 nm. Approximate analytical equations that are valid for cylindrical particles with a length-to-diameter ratio l/d > 3–4 are proposed for calculating the correction factor. More cumbersome formulas of anomalous diffraction must be used at smaller l/d values. It is shown that these formulas transform at the limit into the analytical equations. The spectra of the correction factor for cylindrical and spherical particles are compared. The simple approximation for spherical particles is demonstrated to work well for rather long aggregates when the cylinder volume-to-surface area ratio is the same as for a spherical particle. The results can be used to solve various problems of erythrocyte optics, e.g., to reproduce sizes of aggregates by measuring their spectral absorption.