Active microrheology with a single, time-shared laser trap

Abstract

Recording the mechanical response of biological samples, the cell's interior and complex fluids in general, would enable deeper understanding of cellular differentiation, ageing and drug discovery. Here, we present a time-shared optical tweezer microrheology (TimSOM) pipeline to determine the frequency- and age-dependent viscoelastic properties of biological materials. Our approach consists in splitting a single laser beam into two near-instantaneous time-shared optical traps to carry out simultaneous force and displacement measurements with sub-nanometer and sub-picoNewton accuracy during sinusoidal perturbations. Leveraging numerical and analytical models, we find solutions to commonly encountered deviations, to build an artefact-free nanorheometer. We demonstrate the versatility of the technique by 1) measuring the phase transitions of an ageing biomolecular condensate, 2) quantifying the complex viscoelastic properties of three intracellular compartments of zebrafish progenitor cells, and, using Caenorhabditis elegans, we uncover how mutations causing nuclear envelopathies soften the cytosol of intestinal cells during organismal age. Together, our advances afford rapid phenotyping of material properties inside cells and proteins blends, opening avenues for biomedical and drug screening applications.

Label-Free Techniques for Probing Biomolecular Condensates

“…The aforementioned studies simplify the size and experimental requirement of embedding two beads within the system and expand the approach to smaller droplets. Overall, active microrheology experiments on condensates performed using optical tweezers is actively being employed by several groups. , …”

“…Overall, active microrheology experiments on condensates performed using optical tweezers is actively being employed by several groups. 118,119 Additionally, taking advantage of the optical tweezers ability to directly manipulate objects and detect nanoscale forces, optical tweezers, combined with fluorescence microscopy for imaging, have been used to apply and measure the forces exerted on DNA throughout the entire life cycle (i.e., from nucleation to eventual dissolution or solidification) of the condensate. 112,120−122 Typically these experiments tether the microspheres to long strands of DNA on which condensates can nucleate and condense (Figure 8H,I).…”