Subcellular motions inside live tissue are sensitive indicators of cellular health and cellular response to applied drugs. Digital holography volumetrically captures these motions in tissue dynamics spectroscopy for live-tissue drug screening.
When coherent light scatters from displacing objects, the phase of the light shifts according to the direction and magnitude of motion. When there are many scattering objects, moving in random directions, the phase shifts are added randomly, leading to intensity fluctuations in the scattered light. These intensity fluctuations have statistical properties that relate to the type of motion, with different fluctuation signatures for diffusive vs. directed transport, and with different frequency content for faster or slow motions.
Tissue-dynamics spectroscopy (TDS) combines dynamic light scattering with short-coherence digital holography to capture intracellular motion inside multicellular tumor spheroid tissue models. These spheroids are grown in bioreactors and have a proliferating shell of cells surrounding a hypoxic or necrotic core. The cellular mechanical activity becomes an endogenous imaging contrast agent for motility contrast imaging. Fluctuation spectroscopy is performed on dynamic speckle from the proliferating shell and the hypoxic core to generate drug-response spectrograms that are frequency vs. time representations of the changes in spectral content induced by an applied compound or an environmental perturbation. We have studied a range of reference compounds and conditions applied to multicellular tumor spheroids (MCT) to generate drug fingerprint spectrograms with potential applications in early drug discovery.
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Stewart Center, Purdue University, West Lafayette, IN