Australian researchers make microscopes 20 times more sensitive
gold-nanowire
Image: Quantum Optics Group, ANU

A team at the Australian National University (ANU) in Canberra has used lasers to chill the tiny nanowire probe inside their atomic-force microscope to achieve greater sensitivity for viewing the tiniest of objects. 

Atomic-force microscopy, also known as AFM, is a very high-resolution type of microscopy that can measure nanoscopic structures and the minuscule forces between molecules. The atomic-force microscope was invented in 1986, and this machine was able to produce the first images of the movement of atoms and molecules the world had ever seen.

"Atomic force microscopes are capable of resolutions 1,000 times more detailed than the theoretical limit for optical devices,” says James Maynard at Tech Times. "The tiny nanowire is affixed to a probe on the microscope. As this probe is drawn near the surface of a sample, electromagnetic forces create tiny movements in the nanowire, which are recorded as the ‘shadow’ of the tiniest particles of matter.”

Atomic-force microscopes rely on tiny nanowire probes made from a silver-gallium alloy and coated in gold to produce images. These wires are so fine - about 500 times thinner than a human hair - that they’re prone to shaking simply by being exposed to very mild temperatures.

“At room temperature the probe vibrates, just because it is warm, and this can make your measurements noisy,” said one of the team, Ben Buchler, in a press release. “We can stop this motion by shining lasers at the probe."

The team was able to cool the golden probe to -265 degrees Celsius (-445 degrees Fahrenheit), which allowed for much greater control over the microscope's movements. “The laser makes the probe warp and move due to heat,” adds Giovanni Guccione, a PhD student on the team. "But we have learned to control this warping effect and were able to use the effect to counter the thermal vibration of the probe.”

The researchers published their findings in Nature Communications.

This advancement means atomic microscopes can now detect incredibly subtle forces, and are accurate enough for scientists to sense the weight of a virus that's 100 billion times lighter than a mosquito.

While the microscope can't be used while the laser is cooling down its probe, the team is able to turn the laser off, record their measurements of minuscule subjects super-fast as the probe is heating back up again, and then repeat the process to make sure they’re accurate. 

“We now understand this cooling effect really well,” said one of the team, PhD student Harry Slatyer, in a press release. “With clever data processing we might be able to improve the sensitivity, and even eliminate the need for a cooling laser.”