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Laser cooling allows weighing of viruses

article image The technique uses laser beams to cool a nanowire probe to minus 265 degrees Celsius.

PHYSICISTS at The Australian National University (ANU) have found a way to make atomic force microscopes ultra-sensitive - by using lasers.

The technique uses laser beams to cool a nanowire probe to minus 265 degrees Celsius. This makes the atomic-force microscope probes 20 times more sensitive than normal, allowing them to sense the weight of a large individual virus that is 100 billion times lighter than a mosquito.

The development could be used to improve the resolution of atomic-force microscopes, which are the state-of-the-art tool for measuring nanoscopic structures and the tiny forces between molecules.

Atomic force microscopes achieve extraordinarily sensitivity measurements of microscopic features by scanning a wire probe over a surface. The specific wire probe used by the ANU team was a 200nm-wide silver gallium nanowire coated with gold, around 500 times finer than a human hair.

The sensitivity of the probes are limited by vibration, which introduces noise into measurements.

The laser is used to stop the vibration.

“The laser makes the probe warp and move due to heat. But we have learned to control this warping effect and were able to use the effect to counter the thermal vibration of the probe,” said Giovanni Guccione, a PhD student on the team.

The researchers noted that the probe cannot be used while the laser is on as the laser effect overwhelms the sensitive probe. So the laser has to be turned off and any measurements quickly made before the probe heats up within a few milliseconds. By making measurements over a number of cycles of heating and cooling, an accurate value can be found.

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