ABSTRACTS

Oral Session 1
Monday, October 3
11:10–11:30

Measuring the Refractive Index of Marine Microbes Using a 3D Holo-Tomographic Microscope

The refractive index (RI) of microbes is determined through cellular composition. Knowledge of the internal variability of RI not only reveals the structure within these organisms but is also essential to optically modeling them as well interpreting these models. Due to technical limitations, our current knowledge of RI for these microbes is limited. The Nanolive 3D Cell Explorer is a high precision holo-tomographic microscope that maps the internal structures through their RI based on a rotational interferometric technique to create holographic images. The instrument was calibrated and validated in the lab using materials with known RI values. We measured the RI of marine microbes in near surface waters collected during two experiments, NASA EXPORTS in the North Atlantic in May 2021 and a pre-PACE cruise in the GoM in March 2022. In the collected samples, several microbial groups were identified, including Dinoflagellates, Diatoms, and Cilliates. The internal structures can be clearly differentiated based on RI and a general trend in terms of RI values was observed (chloroplast > membrane). For the external membrane, we were able to identify their composition (Calcium Carbonate vs Silica) based on their measured RI values. We were able to differentiate zooplankton, bacteria, and flocculates composed of sediment aggregates and oil as well. To the best of our knowledge, this is the first time that the internal variations of refractive index within microbes is being directly measured. The results of this study will allow us to better model the optical properties of these marine particles.

Michael Kamowski, University of Southern Mississippi

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