Abstract
Cells sense and respond to mechanical stimuli for activation, proliferation, migration, and differentiation. The associated mechanosensing and biomechanical properties of cells and tissues are significantly implicated in the context of cancer, fibrosis, dementia, and cardiovascular diseases. To gain more mechanobiology insights, dynamic force spectroscopies (DFSs), particularly optical tweezers (OT), have been further advanced to enable in situ force measurement and subcellular manipulation from the outer cell membrane to the organelles inside of a cell. In this review, we first explain the classic OT-DFS rationales and discuss their applications to protein biophysics, extracellular biomechanics, and receptor-mediated cell mechanosensing. As a non-invasive technique, optical tweezers’s unique advantages in probing cytoplasmic protein behaviors and manipulating organelles inside living cells have been increasingly explored in recent years. Hereby, we then introduce and highlight the emerging OT rationales for intracellular force measurement including refractive index matching, active–passive calibration, and change of light momentum. These new approaches enable intracellular OT-DFS and mechanical measurements with respect to intracellular motor stepping, cytosolic micro-rheology, and biomechanics of irregularly shaped nuclei and vesicles. Last but not least, we foresee future OT upgrades with respect to overcoming phototoxicity and system drifting for longer duration live-cell measurements; multimodal integration with advanced imaging and nanotechnology to obtain higher spatiotemporal resolution; and developing simultaneous, automated, and artificial intelligence–inspired multi-trap systems to achieve high throughput. These further developments will grant unprecedented accessibility of OT-DFS and force measurement nanotools to a wider biomedical research community, ultimately opening the floodgates for exciting live-cell mechanobiology and novel therapeutic discoveries.
Highlights
The air condenser (e.g., NA 0.25) projects the forward scattered light onto a second dichroic mirror (DM2, 850SP) [6], which reflects the light to a position detector (PD) like the quadrant photodetector (QPD) after filtering through a neutral density (ND) filter and converging through a planoconcave focusing lens (L3) [3]
Optical tweezers have been demonstrated as a powerful dynamic force spectroscopies (DFSs) technique to study protein–protein interactions in vitro and subsequent cell mechanosensing
The optical tweezers (OT)-DFS and mechanical measurement performance is more sensitive to the environmental drifting and Brownian motion of the trapped beads than to the refractive index of the medium
Summary
In the early 1970s, Arthur Ashkin demonstrated the capability of manipulating dielectric beads using radiation pressure from lasers [1]. The third one measures force via detection of the light momentum change without calibrating trap stiffness [32].
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