First Simultaneous Determination of Size, Refractive Index, Light Scattering Depolarization and Fluorescence of Phytoplankton Cells by Laser Scanning Flow Cytometry

A new laser flow cytometer, based on a laser source of polarized light irradiating microscopic particles, has been developed. The unpolarized and linearly polarized scattered light, as well as the side emitted light in different spectral bands, are measured, allowing the simultaneous and realtime determination of size, refractive index, light scattering depolarization and fluorescence of each particle. Tests with aqueous samples of polystyrene spheres, fluorescent or non fluorescent, and phytoplankton cells demonstrate that the system is able to retrieve size and refractive index and that the light scattering depolarization and fluorescence measurements allows the sorting of particles otherwise indistinguishable.