Photonic force optical coherence elastography for three-dimensional mechanical microscopy

TL;DR

This paper introduces PF-OCE, a novel optical coherence elastography technique that uses phase-sensitive detection to measure three-dimensional mechanical properties of hydrogels with high precision, overcoming limitations of traditional optical tweezers.

Contribution

The study presents a new method combining photonic force and optical coherence elastography for volumetric micromechanical imaging of biological samples, enabling high-throughput and precise measurements.

Findings

PF-OCE accurately measures bead displacements in hydrogels.

Mechanical responses correlate with bulk rheometry measurements.

Method isolates mechanical signals from thermal effects effectively.

Abstract

Optical tweezers are an invaluable tool for non-contact trapping and micro-manipulation, but their ability to facilitate high-throughput volumetric microrheology of biological samples for mechanobiology research is limited by the precise alignment associated with the excitation and detection of individual bead oscillations. In contrast, radiation pressure from a low numerical aperture optical beam can apply transversely localized force over an extended depth range. We propose photonic force optical coherence elastography (PF-OCE), leveraging phase-sensitive interferometric detection to track sub-nanometre oscillations of beads, embedded in viscoelastic hydrogels, induced by modulated radiation pressure. Since the displacements caused by ultra-low radiation-pressure force are typically obscured by absorption-mediated thermal effects, mechanical responses of the beads were isolated after independent measurement and decoupling of the photothermal response of the hydrogels. Volumetric imaging of bead mechanical responses in hydrogels with different agarose concentrations by PF-OCE was consistent with bulk mechanical characterization of the hydrogels by shear rheometry.