Particle sizing and concentration through elastic light scattering at small angles

Elastic light scattering has been used for several decades as an important research tool in biomedicine. The significant interest in light scattering is due as a noninvasive and nondestructive optical tool capable of... [ view full abstract ]

Elastic light scattering has been used for several decades as an important research tool in biomedicine. The significant interest in light scattering is due as a noninvasive and nondestructive optical tool capable of characterize parameters of biological samples. But for biological materials, most of the light is scattered in nearly the forward direction; and low angle light scattering measurements should yield quite accurately the mean cell size value and the concentration per unit area.

Because of this, the angular dependence of light scattering by the sphere-like yeast and lymphocyte cells was measured at angles up to 7°. By illuminating the cell with a converging beam from an inexpensive RGB LED, angularly resolved scattering patterns are imaged by a CMOS sensor and the intensity recorded by a photodetector. The analysis of these patterns with Mie theory leads to the predictions of size distribution of the particles, where we found a mean diameter of 4.0±0.02 μm and the measurable concentration range was ~153 #/μm² to ~226 #/μm² for yeast cells, the measured concentration error was 11.38–14.37%. The measurable concentration range could be adjusted simply by changing the system configuration.

The scattering by the yeast cells was found to agree substantially with the predictions of the Mie equations for the homogeneous sphere, and how properties of the blood cells can be extracted through the light scattering at small angles.