2025-08-20 東京大学
分子振動光熱顕微鏡による細胞内生体分子の熱泳動可視化の概念図
<関連情報>
振動光熱効果を用いたルードヴィヒ・ソレト顕微鏡法 Ludwig–Soret microscopy with the vibrational photothermal effect
Keiichiro Toda and Takuro Ideguchi
Proceedings of the National Academy of Sciences Published:August 14, 2025
DOI:https://doi.org/10.1073/pnas.2510703122
Significance
We introduce vibrational photothermal-induced Soret (ViPS) imaging, an approach extending vibrational microscopy into the study of intracellular thermophoresis—the transport of biomolecules driven by temperature gradients. By combining steady-state optical heating via vibrational photothermal effects with high-resolution refractive index imaging, ViPS reveals previously inaccessible intracellular thermophoretic dynamics. We observed distinct thermophoretic behaviors between the nucleus and cytoplasm, including negative thermophoresis, potentially linked to diffusiophoretic processes. Remarkably, ViPS also captured a significant suppression of thermophoretic activity during the cellular dying process, offering insights into mechanisms of molecular aggregation and glass formation. ViPS imaging substantially enhances the analytical power of vibrational microscopy, opening avenues for investigating intracellular molecular transport.
Abstract
Vibrational microscopy provides label-free, bond-selective chemical contrast by detecting molecular vibrations, making it invaluable for biomedical research. While conventional methods rely on the direct detection of Raman scattering or infrared absorption, recently developed vibrational photothermal (ViP) microscopy achieves chemical contrast indirectly through refractive index (RI) changes. This indirect approach enables unique imaging capabilities beyond traditional chemical imaging. Here, we introduce an application of ViP microscopy: Label-free intracellular thermophoretic (Soret) imaging, which visualizes biomolecular transport driven by temperature gradients. ViP-induced Soret (ViPS) imaging leverages a steady-state temperature distribution generated by optical heating through vibrational photothermal effect, combined with time-resolved RI imaging via optical diffraction tomography. Using ViPS imaging, we measured thermophoretic behavior in living COS7 cells, determining intracellular diffusion and Soret coefficients. Notably, we observed a reversed direction of molecular transport (negative Soret effect) in the cytoplasm compared to the nucleus, possibly driven by thermophoresis-induced diffusiophoresis. Furthermore, time-lapse imaging under CO2-depleted conditions revealed a remarkable reduction in thermophoretic activity, suggesting glass formation during the dying process, likely due to polymer aggregation. ViPS imaging represents a frontier in intracellular thermophoretic studies, expanding the capabilities of vibrational microscopy.
