Exploring light scattering as a streamlined approach to cell system evaluation

The characterization of disperse systems is a critical task across multiple industrial sectors, including biotechnology. Optical density (OD) measurements are frequently used to analyze turbid samples. However, it is not suitable for low-scattering media, such as for example mammalian cell cultures or samples for water quality assessment. In this study, we utilize the measurement of side scattering (90°) from several points along the light beam. This scheme includes highly sensitive light-scattering (nephelometry) principle and in the same time allows to evaluate light attenuation by turbid samples. Although theoretical description of the problem is quite complicated due to multiple scattering, we show that mutual dependence of measurements pertaining to different points obey certain mathematical relations. As a result, during the increase of particle concentration data points move along well-defined trajectory, whose shape is invariant and only the overall scale is controlled by optical parameters of the particles. This result is confirmed experimentally with systems having vastly different parameters including polystyrene beads, silica beads, milk fat globules, E.coli bacteria and mammalian cell lines. We also observed signs of trajectory alteration due the change of individual cells' optical parameters during culture growth. Our findings demonstrate that the described light scattering analysis enables monitoring of particle and cellular systems, highlighting its potential as a practical, adaptable, and cost-effective approach.