Scientists make light of micro-manipulation

Updated: 6:12 p.m. ET July 20, 2005

LONDON - Scientists seeking a simple solution to the tricky task of separating single cells from a herd of others have found a way of making light of the problem.

The new technique dubbed the "optoelectronic tweezer" combines a relatively low intensity light source with photo electricity to allow scientists to literally corral the cells they want to study, and could have major medical implications.

"Our design has a strong practical advantage in that, unlike optical tweezers, a simple light source such as a light-emitting diode ... is powerful enough," said Pei Yu Chiou, part of the team led by Ming Wu at the University of California, Berkeley.

The new technique, reported in the science journal Nature, could be used to quickly isolate and study foetal cells in a mother's blood sample or separate abnormally shaped organisms from healthy ones.

As opposed to optical tweezers which use lazer beams to round up cells, the low intensity light source which uses 100,000 times less power than that needed for a lazer makes sure there is no risk of damage to neighbouring cells.

Currently the process is manual and time-consuming, involving a technician finding the cell of interest under a microscope and literally cutting out the piece of the slide where it is.

The new process, which works on the same basis as a photocopier by attracting the wanted cells to a specific spot, can not only isolate large numbers very quickly but could in future be linked to a computer and automated.

A batch of cells are sandwiched between a piece of glass and a photoconductive surface and a beam of light is played across the surface.

Depending on the properties of the cells being studied — for example dead and living cells have different conductivity — the cells will either be attracted to or repelled by the light, making it easy for scientists to move them where they want to.

In one experiment, the Berkeley team produced a grid of 15,000 traps each containing one particle in a grid measuring just 1.3 by 1.0 millimetres.

So flexible is the technique that the scientists can sort the particles into different patterns and different sizes almost at the flick of a switch for ease of study.

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