Assessment of Small Cellular Particles from Four Different Natural Sources and Liposomes by Interferometric Light Microscopy

Abstract

Small particles in natural sources are a subject of interest for their potential role in intercellular, inter-organism, and inter-species interactions, but their harvesting and assessment present a challenge due to their small size and transient identity. We applied a recently developed interferometric light microscopy (ILM) to assess the number density and hydrodynamic radius (R_h) of isolated small cellular particles (SCPs) from blood preparations (plasma and washed erythrocytes) (B), spruce needle homogenate (S), suspension of flagellae of microalgae <i>Tetraselmis chuii</i> (T), conditioned culture media of microalgae <i>Phaeodactylum tricornutum</i> (P), and liposomes (L). The aliquots were also assessed by flow cytometry (FCM), dynamic light scattering (DLS), ultraviolet-visible spectrometry (UV-vis), and imaging by cryogenic transmission electron microscopy (cryo-TEM). In R_h, ILM showed agreement with DLS within the measurement error in 10 out of 13 samples and was the only method used here that yielded particle density. Cryo-TEM revealed that representative SCPs from <i>Tetraselmis chuii</i> flagella (T) did not have a globular shape, so the interpretation by R_h of the batch methods was biased. Cryo-TEM showed the presence of thin filaments in isolates from <i>Phaeodactylum tricornutum</i> conditioned culture media (P), which provides an explanation for the considerably larger R_h obtained by batch methods than the sizes of particles observed by cryo-TEM images. ILM proved convenient for assessment of number density and R_h of SCPs in blood preparations (e.g., plasma); therefore, its use in population and clinical studies is indicated.