Laser physicists in Australia have come up with a new way to boost the sensitivity and measuring capability of atomic force microscopes.
The technique, which is described in a study published in the journal Nature Communications on Aug. 14, makes use of laser cooling and could improve the sensitivity of atomic force microscope probes by up to 20 times and make them more adept at identifying tiny forces as seemingly weightless as one virus.
Scientists from the Research School of Physics and Engineering at The Australian National University (ANU) in Australia, who conducted the study, said that they were able to improve microscope sensitivity by cooling nanowire probes to minus 265 degrees Celsius using laser beams.
Atomic force microscopes are used to examine very tiny structures and forces between molecules. Taking measurements involves scanning a nanowire probe over a surface but the problem with these probes, which are about 500 times finer than human hair, is that they are prone to vibration.
Study researchers Ping Koy Lam, from the Research School of Physics and Engineering at ANU, said that the probe vibrates at room temperature simply because it is warm and this results in measurements to be noisy. The researchers were able to do something about this by shining laser beams at the probe so it cools to minus 265 degrees Celsius and thus allow the microscope to have more accurate sensitivity to weight.
"Here we show broadband multimode cooling of -23 dB down to a temperature of 8±1 K in the stationary regime," the Ping Koy Lam and colleagues wrote. "Through the use of periodic quiescence feedback cooling, we show improved signal-to-noise ratios for the measurement of transient signals."
Ping Koy Lam said that employing the laser cooling technique resulted in sensitivity good enough for them to detect the weight of a large individual virus that weighs 100 billion times lighter than a mosquito.
The researchers, however, acknowledged that there are still problems with the new technique. For one, the probes heat up quite fast after it has cooled and this means that measurements have to be made very fast- in a matter of a few milliseconds. The researchers, however, consider doing predictive measurement so they do not become too reliant on using laser in every test.
"If you imagine that during one time period you just observe the motion of the wires, that gives you information that in the next time period you use to [predict] something," Ping Koy Lam said. "By observing the period before, you can predict if there was anything present to cause the wire to behave in a certain way, for example."
