Video-rate volumetric chemical imaging via mid-infrared photothermal optical diffraction tomography

Label-free vibrational microscopy provides chemically specific access to cellular structures, yet quantitative volumetric imaging of intracellular dynamics remains challenging on subsecond timescales. Here, we demonstrate video-rate mid-infrared photothermal optical diffraction tomography (MIP-ODT) by combining high photothermal sensitivity with rapid angular scanning. The system achieves 19.2 volumes per second, nearly 400 times faster than previous MIP tomography implementations, with a signal-to-noise ratio exceeding 70 and no temporal averaging. We track lipid droplets in living cells and quantify anomalous diffusion from three-dimensional trajectories, revealing heterogeneous intracellular transport behaviors obscured in two-dimensional measurements. Rapid mid-infrared wavenumber sweeping further enables broadband multi-wavenumber volumetric chemical imaging across a 300 cm⁻¹ spectral window within 1 s. These results establish MIP-ODT as a platform for high-speed, label-free volumetric chemical imaging of single cells and quantitative investigation of dynamic intracellular organization.