Optical trapping
TOMOTRAP (Tomographic Mould for Optical Trapping)
Stable orientation/position control of non-spherical particles based on real-time 3D refractive index distribution measurements
(Nature Communications, 2017)
(left) 3-D rendered isosurfaces of a PMMA dimer which orientation is controlled by TOMOTRAP. The dimer is rotated with respect to the z-, x-, and y- axis in desired orientation.
(center) 3-D rendered isosurfaces of a red blood cell (RBC) which orientation and shape are controlled by TOMOTRAP. The RBC is first rotated with respect to the x-and z- axis, and the RBC is folded to L-shape. The folded RBC is then rotated with respect to the z-axis while maintaining L-shaped folding.
(right) 3-D rendered isosurfaces of two red blood cells (RBCs) which orientation and position are controlled by TOMOTRAP independently. Initially, two RBCs are sedimented on a cover glass with face-on orientation. TOMOTRAP independently rotates each RBC with respect to the x- and y-axis of the center of mass of each RBC sequentially, and translates two RBCs to assemble them as a T-shaped complex of RBCs consisted of two RBCs in edge-on orientation. The assembled RBCs are then rotated with respect to the z- and x-axis sequentially, and the final orientation of the RBCs is one face-on and one edge-on.
Working principle of TOMOTRAP
Combination of 3-D refractive index measurements and wavefront shaping technique
a, Schematic diagram of TOMOTRAP. Initially, the 3-D RI distribution of samples is measured by real-time optical diffraction tomography (b). From measured tomograms, the desired 3-D shape of samples is calculated by applying translation, rotation, or folding transformation. Next, the wavefront of the trapping beam is calculated from the desired 3-D shape of samples by applying 3-D Gerchberg-Saxton algorithm (c). This calculated wavefront will give arise to a 3-D beam intensity shape that is identical to the 3-D volumes of samples. Then, the calculated wavefront is displayed onto a sample, and this maximizes the overlapping volume between the samples and the trapping beam intensity. Finally, the samples are aligned with the updated orientation and morphology in three dimensions as intended. d, Time-lapse images of the assembly of two RBCs using TOMOTRAP. Scale bar indicates 5 μm.
a-b, We trapped eight silica beads forming a rotating cube by holographic optical tweezers, and tracked 3-D positions of silica beads in Brownian motion for 1.7 sec after the release of the trapping beam by optical diffraction tomography measured at the frame rate of 60 Hz, as shown in 3-D rendered isosurfaces of the RI maps of the beads (a), and time-lapse trajectories of the beads under Brownian motion (b). c, 3-D tracking of a macrophage and an optically trapped silica bead measured by bright-field imaging (top), the angular spectrum method of measured holograms (middle), and optical diffraction tomography (bottom). The locations of the bead are indicated with black arrows. d, Consecutive time-lapse cross-sectional slices in c. © The Optical Society