Tweezers offer point and drag control

23 Mar 2005

Biologists benefit from 4D optical tweezers that move cells in real-time at the touch of a computer mouse.

Scientists in Denmark have developed an optical manipulation system that moves tiny particles in 3D in real-time at the click of a mouse button. The computer-controlled “4D optical tweezers” are the brainchild of Jesper Glückstad and his co-workers from Risø National Laboratory in Roskilde (Applied Physics Letters 86 074103).

3D arrangements

“Up to 80 particles have now been simultaneously manipulated by point and drag of a simple PC mouse interface with less than a Watt of near-infrared laser light,” Glückstad told Optics.org. “In addition, we are now able to view in 3D while manipulating -- this capability is unique since it allows full visualization and therefore precise position and velocity control.”

The system works by converting a 830 nm laser beam from a Ti:Sapphire laser into an array of independently-controlled optical traps that can move multiple particles simultaneously. The traps are made by passing the TEM₀₀ beam through a computer-controlled spatial light modulator (SLM) and spatial polarization modulator (SPM). By changing the phase and polarization encoding in the SLM and SPM it is possible to reconfigure the traps in real-time.

sphere signature

To demonstrate the potential of the technique the team have assembled tiny (2-3 micron diameter) polystyrene and SiO2 spheres into all kinds of 3D arrangements, including a pyramid and a series of letters.

However, the system could have important real-life applications in biology and physics. Glückstad says that it could prove useful for sorting cell colonies, seeding crystal growth and assembling photonic crystals among other tasks. It has already been used to isolate a particular species of yeast cell and demonstrate the effect of confinement on its growth.

“The true 4D capability [3D manipulation in real-time] enables real-world experiments by microbiologists and material scientists,” he commented. “Stem cell science is an obvious application as are fertility studies and blood cell analysis.”

Author
Oliver Graydon is editor of Optics.org and Opto & Laser Europe magazine.