Realization of Planar Optical Tweezer (2D-LOT) Powered by Light Sheet
arxiv(2024)
Abstract
We report the realization of the first planar optical tweezer trap system by
a sheet of light. To visualize the trapping of the target object (dielectric
bead or live cell) in a plane, an orthogonal widefield detection is employed.
The planar / two-dimensional lightsheet optical tweezer (2D-LOT) sub-system is
realized in an inverted microscopy mode with illumination from the bottom. A
1064 nm laser (power ∼ 500 mW) is expanded and directed to a combination
of cylindrical lens and high NA objective lens to generate a tightly-focused
diffraction-limited light sheet. The object to be trapped is injected in the
specimen chamber (consists of two coverslips placed at a distance of ≈
1 mm) using a syringe. The illumination of trap-laser light is along
Z-direction (with coverslip along XZ-plane) whereas, the detection is achieved
perpendicular to the coverslip (along Y-axis). The orthogonal detection is
employed to directly visualize the trapping in a plane. The characterization of
system PSF estimates the size of light sheet trap PSF to be, 2073.84 μ m^2
which defines the active trap region / area. Beads are tracked on their way to
the trap region for determining the trap stiffness along Z and X i.e, k_z =
1.13 ± 0.034 pN/μ m and k_x = 0.74 ± 0.021 pN/ μ m. Results (image
and video) show real-time trapping of dielectric beads in the trap zone (2D
plane) generated by the light sheet. The beads can be seen getting trapped from
all directions in the XZ-plane. Prolonged exposure to the light sheet builds up
a 2D array of beads in the trap zone. Similar experiments on live NIH3T3 cells
show cells trapped in the 2D trap. The potential of the planar trap lies in its
ability to confine objects in two dimensions, thereby opening new kinds of
experiments in biophysics, atomic physics, and optical physics.
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