With a suitably formed light beam, matter can be caught, held, and moved – this is a simple explanation of how optical tweezers work. The technique is non-invasive and sterile, making it suitable for biological research into areas such as cancer cells.

At Wrocław University of Science and Technology, this method is being developed by University Professor Sławomir Drobczyński, PhD, Dsc, Eng. from the Department of Optics and Photonics. In his laboratory, he researches the development and applications of optical tweezers. The researcher has developed an advanced optical manipulator system to combine optical trapping with various microscopic imaging techniques.

– I came across the phenomenon of optical trapping many years ago during a research placement at the University of Strasbourg. I decided to explore this issue further and continue my research at Wrocław University of Science and Technology – says Prof. Sławomir Drobczyński.

He adds that he was fascinated by both the phenomenon itself and the apparatus used to observe it. – As I’m a graduate of a technical university, what I always have in the back of my mind is an engineer’s question about how a given device is constructed and how it can be further improved – says the WUST scientist.

He explains that the laser beam can act as tongs to manoeuvre small particles, of micro- or even nanometre sizes.

– It’s a completely sterile method, without mechanical contact involved, which is why it is perfect as a tool in molecular biology, making it possible, for example, to stretch and measure the elasticity of DNA strands – explains Prof. Drobczyński.

The instrumentation he constructed is used in an interdisciplinary project funded by the National Centre for Science, which also involves Wrocław Medical University and the Institute of Low Temperature and Structure Research of the Polish Academy of Sciences. Using optical tweezers and microrobots, scientists examine cancer cells subjected to hyperthermia.

Single-cell heating

Professor Sławomir Drobczyński: – Hyperthermia is a technique for the controlled heating of cancerous lesions. The point is that cancer cells are more sensitive to increased temperatures, so they can be “overheated” and destroyed more easily. Having said that, the question arises as to how to control this process in such a way that healthy cells aren’t destroyed. It’s also not known whether all cancer types respond to hyperthermia to an equal extent.

The researchers set out to design micro-tools that would generate heat using light and measure temperature to follow the process of programmed cell death in real-time in an “in vitro” tumour model. To do this, they use micro-robots whose functionality depends on the parameters of the laser beams illuminating them.

– Thanks to optical tweezers, we can selectively grasp micro-sized objects, including cells, clusters of cells, or microrobots acting as heat generators as well as thermometers – elaborates the WUST scientist. – In a microscope preparation, we use light to grasp a micro-thermometer and a “heater” to bring them close to the cell, observing what happens when a given spot is heated – he explains.

As far as the biological side is concerned, the research is supported by Kamila Duś-Szachniewicz, MD, PhD. from the Department of Pathomorphology at Wrocław Medical University, while the team led by Prof. Artur Bednarkiewicz from the Institute of Low Temperatures and Structural Research at the Polish Academy of Sciences is responsible for developing the micro-robots.
The research is expected to help understand the pathophysiology of cancer cells but also contribute to the development of effective targeted therapy.

The power of light

Professor Drobczynski emphasises that the laboratory can be used to research a variety of materials, not just biological ones. The device is suitable, too, for observing many micro-scale physical phenomena.

– Very small displacements and forces can be measured. I cooperate with Jakub Ślęzak, PhD. from WUST’s Faculty of Mathematics, who is a specialist in the mathematical analysis of models used to describe optical traps. We’re extremely interested in the modelling and experimental verification of the behaviour of microscopic objects in the presence of light beams with different parameters – says the WUST physicist.

The researcher emphasises that when the apparatus was being developed, a lot of time was spent making sure it would bed user-friendly. Among other things, he used a touch screen linked to the laser beam control system. With an interactive interface, by swiping your finger on the monitor displaying an image of a microscope preparation, you move the laser beam.

– What you do on the monitor happens in real-time in the preparation – says the Professor. He adds that if you choose the right wavelength and power, the tweezers can act as a laser scalpel, with which you can deliberately damage something in the material under examination.

– The use of light and optical phenomena in today's highly advanced technologies and research defines modern optics, without which super-fast telecommunications would not exist, to give you a quick example. Researchers around the world are discovering more and more new applications for optics in metrology. I’m happy to be able to establish cooperation with biologists, chemists, as well as mathematicians and physicists – concludes Prof. Sławomir Drobczyński.