WUR researchers make smallest force measurement ever

Researchers of the Physical Chemistry and Soft Matter group have developed a method to measure ultra-small forces on a single molecule. It is the smallest force measured to date. With these measurements, scientists can gain new insights into various biological processes, such as the growth of plants. The method can also be used in the…

The measurements are performed with special molecules that emit light when force is exerted on them. © Illustration: Barend Wilschut

With this new method, the researchers have accomplished something that was previously considered impossible. Until now, scientists could only measure whether a force was exerted on molecules or not. ‘With this new method, mechanical forces are not black-and-white anymore, but can be measured in 50 shades of grey’, says Joris Sprakel of the Physical Chemistry and Soft Matter group. Additionally, much smaller forces can be measured now, even at the level of a single molecule. Sprakel: ‘Let’s say that a molecule would be the size of a human. This would be comparable to measuring whether you have a grain of sand on your shoulder from a distance, and even telling you exactly how big that grain of sand is.’

New possibilities

The method opens many paths to new research, says Sprakel. ‘Scientists know that these forces play a part in many processes, but as the forces could not be measured exactly – or at all, even – they were not able to study them properly. With this method, we can literally shed some light on these processes, to better understand how things work.’

Mechanical forces surround us, Sprakel continues. ‘They ensure that you feel something when pushing an object, for example. The same applies to molecules, but the forces are much, much smaller. With these nudges, the molecules can react to one another, which determines the properties of a material. These forces make it possible to contract my muscles when I push on a table, but they also keep the table stable, stopping me from pushing through its surface.’

Plant embryos and space travel

There are already plans for follow-up research. Together with Biochemistry professor Dolf Weijers, Sprakel and his team want to study how these forces influence the development of plant embryos. Sprakel is also collaborating with Delft University of Technology on the further development of self-healing materials for space craft. ‘Research is often largely trial and error. If we can discover the exact mechanics, it will allow us to better focus development and improvements.’

Postdoc Ties van de Laar and master’s student in Molecular Life Sciences Evelien Heusinkveld (both part of the research team) inspecting a measurement. ©Tessa Louwerens


According to Sprakel, the development of the method was quite a challenge. The forces are measured using special molecules which the researchers have designed to fluoresce whenever a force is exerted on them. This light is subsequently measured, enabling the researchers to see exactly how much force was exerted. ‘It was very difficult to build a setup that can measure a single molecule, as that produces very little light’, Sprakel elaborates. On top of that, they only had a very limited budget; nobody believed in the research proposal. His team was forced to build the setup MacGyver style. ‘Within our team, we have people with various expertise. I don’t think we would have been able to pull it off without this collaboration.’

You can read the publication here.

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