Influence from Anisotropic Silica Particles in Flow Cytometry

Abstract

When it comes to shape, most of bacteria have the rod-like shape giving them the one of the most significant characteristics differentiated from human blood cells. On the other hand, red blood cells have the disk-like shape. This research was focused on increasing sensitivity for bacteria exclusively. Dependence on the shape of particles for signal intensity has been investigated, which was conducted with the modelling system by using silica particles. Isotropic sphere silica particles representing human red blood cells with three different sizes and anisotropic rod-like silica particles representing bacteria were synthesized. The synthesized particles were analyzed with a scanning electron microscope (SEM) and dynamic light scattering (DLS). Samples containing sphere or rod-like particles themselves or their mixtures were measured by using a flow cytometer for the height data of forward scatter (FSC-H), which indicates intensity of signals. Although radius of gyration (Rg) of rod-like particles is bigger than those of sphere particles, it has weaker intensity. This is due to anisotropy of rod-like particles. Since a sphere particle is isotropic, its scattering pattern is concentric circles with the maximum signals at the center keeping most forward scattered signals within the detecting area. In contrast, an anisotropic rod-like particle forms two symmetric lobes when scattering. Hence, most of forward scattered signals escape the detecting area. In addition, flow cytometry experiments with different ratios of isotropic particles to anisotropic particles were also carried out for sensitivity of detection on anisotropic rod-like silica particles. It is detectable for anisotropic rod-like particles up to the ratio of 10:1. Therefore, the results suggest the possibility to distinguish between red blood cells and bacteria.