Research Highlight

Eavesdropping on cell interactions

doi:10.1038/nindia.2012.57 Published online 23 April 2012

Researchers have used high power 'near-infrared' laser light to trap microspheres of polystyrene beads, which could find use in probing the interactions between biological cells.

They trapped the microspheres in a tiny chamber formed by a cover slip and a glass slide.

In recent years, focused laser beams have emerged as handy tools for trapping and studying micrometre-scale materials. The tiny force exerted by such a beam induces random self-assembly of microparticles, thus providing an insight into the dynamic of particles in a well-understood force environment.

The researchers explored ordered self-assembly by employing a single pure Gaussian beam emitted by a near-infrared laser. They used an inverted microscope to focus the beam onto a sample chamber formed by a cover slip and a glass slide. The sample chamber contained spherical beads of polystyrene dispersed in water.

Slight manipulation of the microscope focus caused spherical aberrations in the cover slip that pushed the beads towards the edge, leading to the formation of well-defined closed ring structures. Switching off the optical trap caused the beads to diffuse away, only to reassemble almost instantaneously in the same ring structure after the trap was switched on again.

Each bead measured 1.1 μm and assembled into a ring-like structure with a diameter of 3–5 μm. The rings contained 9–15 spherical beads. The radii of the rings could be varied by changing the focus of the laser beam.

"The ring pattern can be useful for studying tiny interaction forces between microparticles and the controllable study of biological cell-to-cell interactions, such as that between cancer cells and natural killer cells," says lead researcher Ayan Banerjee.


  1. Haldar, A. et al. Self-assembly of microparticles in stable ring structures in an optical trap. Phys. Rev. A 85, 033832 (2012) | Article | ADS |