Multi-wavelength spectroscopy of oriented erythrocytes

Accurate characterization of the optical properties of erythrocytes is essential for the applications in optical biomedicine, in particular, for diagnosis of blood related diseases. The observed optical properties strongly depend on the erythrocyte's size, hemoglobin composition and orientation relative to the incident light. We explored the effect of orientation on the absorption and scattering properties of erythrocytes suspended in saline using UV-visible spectroscopy and theoretical predictive modeling based on anomalous diffraction approximation. We demonstrate that the orientation of erythrocytes in dilute saline suspensions is not random and produces consistent spectral pattern. Numerical analysis showed that the multi-wavelength absorption and scattering properties of erythrocytes in dilute suspensions can be accurately described with two orientation populations. These orientation populations with respect to the incident light are face-on incidence and edge-on incidence. The variances of the orientation angles for each population are less than 15 degrees and the relative proportions of the two populations strongly depend on the number density of the erythrocytes in suspensions. Further, the identified orientation populations exhibit different sensitivities to the changes in the compositional and morphological properties of erythrocytes. The anomalous diffraction model based on these orientation populations predicts the absorption and scattering properties of erythrocytes with accuracy greater than 99%. Establishment of the optical properties of normal erythrocytes allows for detection of the disease induced changes in the erythrocyte spectral signatures.