'Optical tweezers' could help study living cells

Researchers will soon be able to study biological changes at scales and speeds not previously possible, as physicists at The University of Queensland (UQ) have used so-called ‘tweezers made from light’ to measure activity within microscopic systems over timeframes as short as milliseconds.

Published in the journal Optica, the UQ method involved creating ‘ballistic rotating optical tweezers’ — by shining a laser through a microscope and controlling its polarisation — to trap tiny probes that rotate in the fluids of the samples being studied and measure their rotation at exceedingly short timescales.

“How the probes rotate and interact with the surrounding environment allows us to track changes in properties like the viscosity of fluid within a biological cell,” PhD candidate Mark Watson explained.

“After the light goes through the petri dish, we collect it and based on how the light has been changed, we can determine what’s happened.

“With these tweezers made from light, we are able to apply pressure and grab microscopic items and turn them around, just like you would with physical tweezers in much larger environments.”

Having proven the method works, the researchers are on the cusp of testing it in single living cells, which would be a boon for biologists.

“For example, they will be able to look at how a cell is dividing, how it responds to outside stimuli, or even how chemical reactions affect cell properties,” said UQ’s Professor Halina Rubinsztein-Dunlop.

“Any development of a medical condition could be dependent upon the dynamic processes inside, say, cancer cells versus healthy cells on very short timescales.

“Making that knowledge available opens up the possibility of new drugs and ways to deliver them, or tests to see whether a cell is functioning as it should.”

Dr Alexander Stilgoe added that the method would be able to track dynamic changes in cells and systems on timescales existing methods had struggled to capture and had done so with better resolution. He said the optical tweezers could also help researchers answer longstanding questions about much larger phenomena.

“Behaviour or movement in crowds, or patterns forming in large flocks of birds in the sky have so far escaped understanding,” Stilgoe said.

“If we bring that to a nano or microscale, such as by observing similar behaviour in swimming bacteria, we might be able to resolve some of the questions that have remained unanswered for centuries.”

Image caption: Itia Favre-Bulle, Halina Rubinsztein-Dunlop, Alexander Stilgoe and Mark Watson.