17 September 2009

Table tennis in a Petri dish

The new device plays ping pong with live cells

The original system of holding and controlling the movement of cells during operation resembles an old video game of "flat" ping-pong, but it is not intended for entertainment at all. A bright achievement was announced by a group of scientists specializing in micro devices combining optical, magnetic and electrical components from the Optoelectronic Biofluidic Laboratory at the University of California at Los Angeles, led by Pei-Yu Chiou.

The new miniature device is a plate covered with glass, with a free space between them, in which microscopic particles float to be studied – for example, living cells.

With the help of a laser, any movable drawings are formed on the surface of the device, serving as virtual "walls" holding cells in specified positions or moving "wards" between them. However, light does not act directly on cells at all, and this is the beauty of Chiou and his team's invention.

Laser systems for holding micro-objects have been known for a long time, but they are not suitable for biological research. The fact is that for reliable manipulation of tiny bodies, very bright rays with a flow of energy of megawatts per square centimeter are needed. And they risk just burning the cells.

Another way of manipulating living objects – electric fields – is more gentle, but the accuracy leaves much to be desired. Therefore, researchers from the USA decided to build a more successful version of the "superpincet".

The new high-tech Petri dish is a combination of both principles that has given scientists new opportunities. The bottom of this "cup" is covered with a grid of photodetectors, and two translucent electrodes are placed above each such cell – one at the bottom and one at the top.

When the light hits the detector, an external voltage source is connected to the electrodes. It is the electric field that shifts living cells, and not the laser itself, whose power may be small and does not disturb the "test subjects".

But with a laser, you can draw a variety of lines and circles within the "cup", forcing cells to move under the pressure of these "light walls". Moreover, the device makes it easy to separate and group single cells and control the movement of each of them individually – just a small step of "pixels" is responsible for this.

This system will be useful for biological research, including those where long–term cell cultivation is required under controlled conditions, the authors of the device believe. The scientists presented the details of their development in an article in the journal Lab on a Chip.

Source: New Scientist

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