Optical tweezers are an invaluable tool for non-contact trapping andmicro-manipulation, but their ability to facilitate high-throughput volumetricmicrorheology of biological samples for mechanobiology research is limited bythe precise alignment associated with the excitation and detection ofindividual bead oscillations. In contrast, radiation pressure from a lownumerical aperture optical beam can apply transversely localized force over anextended depth range. We propose photonic force optical coherence elastography(PF-OCE), leveraging phase-sensitive interferometric detection to tracksub-nanometre oscillations of beads, embedded in viscoelastic hydrogels,induced by modulated radiation pressure. Since the displacements caused byultra-low radiation-pressure force are typically obscured byabsorption-mediated thermal effects, mechanical responses of the beads wereisolated after independent measurement and decoupling of the photothermalresponse of the hydrogels. Volumetric imaging of bead mechanical responses inhydrogels with different agarose concentrations by PF-OCE was consistent withbulk mechanical characterization of the hydrogels by shear rheometry.
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