Laser tweezers manipulation of diatom chloroplasts and intracellular viscosity evaluation

Abstract

The advancement of optical tweezers has revolutionized biological research, enabling precise manipulation of microscopic objects. In this study, we applied optical tweezers to diatom algae, known for their intricate silica frustules, achieving precise manipulation of their cells and chloroplasts. We demonstrated the ability to trap and move chloroplasts within cells of diatom Coscinodiscus oculus-iridis without causing damage, revealing the role of cytoplasm in maintaining organelle connectivity and facilitating motion. Using optical tweezers, we measured intracellular viscosity across different cytoplasmic regions, revealing a broad range influenced by local environment and cell-to-cell variability. These values reflect the viscosity of an equivalent continuous medium that would produce the same viscous friction coefficient for chloroplast movement. Although these data likely overestimate the true cytoplasmic viscosity—due to boundary layer interactions and the influence of cytoplasmic strands—they provide valuable insight into intracellular mechanics. Additionally, the achieved manipulation of entire diatom cells, including cells undergoing division, highlights the mechanical resilience of their silica frustules under external forces. These findings not only advance our understanding of diatom biology but also lay the groundwork for applications in biomimetic materials, photonic systems, and environmental research.