Label-free imaging of cellular organization in living mammalian cells via external apodization phase-contrast microscopy

Developing techniques to visualize the dynamics of cellular organization, which impacts the spatiotemporal functionality of biomolecules, is essential for elucidating mechanisms that govern cellular behavior. In this study, we demonstrated that label-free external apodization phase-contrast (ExAPC) microscopy is a valuable modality for this purpose, as this method can be used to visualize refractive index changes in intracellular structures, achieves high spatiotemporal resolution and suppresses halos. Utilizing the ability of ExAPC microscopy to visualize various intracellular structures simultaneously, we successfully captured detailed alterations in cellular organization during diverse cellular behaviors. Furthermore, through quantitatively analyzing the images obtained by combining ExAPC microscopy with fluorescence microscopy, we discovered characteristic heterogeneities in biomolecular condensates, lipid droplets, and mitochondria. This study underscores the potential of ExAPC microscopy for providing detailed images of alterations in cellular organization associated with various cellular behaviors, thereby corroborating the existing knowledge and potentially revealing novel discoveries.