New Laser Method Causes Microscope to be 20 Times More Powerful

A laser may just make an atomic-force microscope probe 20 times more sensitive. Scientists have found a way to make these microscopes powerful enough to detect forces as small as the weight of an individual virus.

Atomic force microscopes achieve sensitivity measurements of microscopic features by scanning a wire probe over a surface. However, probes are prone to vibration due to their size-about 500 times finer than a human hair.

"At room temperature, the probe vibrates, just because it is warm, and this can make your measurements noisy," said Ping Koy Lam, co-author of the new paper, in a news release. "We can stop this motion by shining lasers at the probe."

In this case, the researchers used a force sensor that was a 200 nm-wide silver gallium nanowire coated with gold. The laser made the probe warp and move due to heat, but the scientists controlled this warping effect and were able to use it in order to counter the thermal vibration of the probe.

"The level of sensitivity achieved after cooling is accurate enough for us to sense the weight of a large virus that is 100 billion times lighter than a mosquito," said Ben Buchler, one of the researchers.

That said, the probe can't be used while the laser is on, since the laser effect overwhelms the sensitive probe. This means that the laser has to be turned off and any measurements quickly made before the probe heats up within a few milliseconds.

"We now understand this cooling effect really well," said Harry Slatyer, one of the researchers. "With clever data processing we might be able to improve the sensitivity, and even eliminate the need for a cooling laser."

The findings are published in the journal Nature Communications.