Phase contrast tomography (PCT)

Phase contrast microscopy has been fundamental to 2D imaging of transparent specimens since its invention. Here, we report phase contrast tomography (PCT), a label-free 3D refractive-index imaging technique that, for the first time, integrates quantitative phase contrast microscopy with the Fourier diffraction theorem. PCT achieves a lateral resolution of 270 ± 9 nm and an axial resolution of 890 ± 42 nm, with a volumetric imaging rate of 3 Hz. This approach represents a paradigm shift that extends the intrinsic stability, common-path robustness, and high signal-to-noise ratio of conventional 2D phase contrast imaging into the realm of 3D refractive-index reconstruction. We demonstrate PCT's capability by capturing mitochondrial cyclization in live COS7 cells treated with 500 μM CCCP, as well as by performing 3D single-particle tracking of lipid droplets in live COS7 cells, revealing spatially balanced intracellular diffusion unaffected by gravity. PCT establishes a powerful and versatile platform for probing dynamic biological processes in three dimensions.