Scientists in Sweden have developed a simple method to make the universe’s normally invisible binding forces visible by using gold flakes, salt water and light. The Chalmers University of Technology team created a platform that displays these tiny forces—often described as “nature’s invisible glue,” responsible for effects like dust sticking to surfaces or lizards climbing walls—as shifting colors. The technique offers a faster, more accessible way to study how matter organizes itself at the smallest scales.
Inside the lab, doctoral student Michaela Hošková holds up a small glass container filled with millions of micrometer-sized gold flakes suspended in a salt solution. Using a pipette, she places a droplet of the mixture onto a gold-coated glass plate positioned under an optical microscope. The flakes are immediately drawn toward the surface but stop just short of fully attaching, leaving nanometer-sized gaps between the flakes and the gold substrate.
These tiny liquid-filled gaps act like miniature light chambers. Light reflects back and forth inside them, producing visible colors. When the setup is illuminated with a halogen lamp and the reflected light is analyzed with a spectrometer, the different wavelengths become clear. On the connected monitor, flakes shimmer and shift in colors such as red and green against a golden yellow background.
“What we are seeing is how fundamental forces in nature interact with each other. Through these tiny cavities, we can now measure and study the forces we call ‘nature’s glue’ – what binds objects together at the smallest scales. We don’t need to intervene in what is happening, we just observe the natural movements of the flakes,” says Michaela Hošková, a doctoral student at the Department of Physics at Chalmers University of Technology.
By examining the light captured in the cavities, the team can analyze the balance between two competing forces – one that pulls the flakes together and one that keeps them apart. The attractive force, known as the Casimir effect, causes the gold flakes to move toward each other and toward the surface. The opposing electrostatic force develops in the salt solution and prevents the flakes from fully sticking. When these forces reach equilibrium, a process called self-assembly occurs, forming the cavities that make the measurements possible.
“Forces at the nanoscale affect how different materials or structures are assembled, but we still do not fully understand all the principles that govern this complex self-assembly. If we fully understood them, we could learn to control self-assembly at the nanoscale. At the same time, we can gain insights into how the same principles govern nature on much larger scales, even how galaxies form,” says Michaela Hošková.
The new platform builds on several years of research in Professor Timur Shegai’s group at the Department of Physics. Four years ago, the team showed that a pair of gold flakes could form a self assembled resonator. They have now expanded that discovery into a broader method for investigating fundamental forces.
In this system, the gold flakes function as tiny floating sensors. According to the researchers, the approach could be valuable across physics, chemistry, and materials science.
“The method allows us to study the charge of individual particles and the forces acting between them. Other methods for studying these forces often require sophisticated instruments which cannot provide information down to the particle level,” says research leader Timur Shegai.
The platform may also help scientists better understand how particles behave in liquids, including whether they remain stable or tend to clump together. That knowledge could improve how medicines move through the body, support the design of more effective biosensors, and contribute to better water filtration systems. It is also relevant for everyday products such as cosmetics, where preventing unwanted clumping is essential.
“The fact that the platform allows us to study fundamental forces and material properties shows its potential as a truly promising research platform,” says Timur Shegai.
In the laboratory, Hošková opens a small box containing a finished version of the device. Using tweezers, she places it into the microscope. Two thin glass plates enclose everything needed to examine nature’s invisible glue.
“What I find most exciting is that the measurement itself is so beautiful and easy. The method is simple and fast, based only on the movement of gold flakes and the interaction between light and matter,” says Michaela Hošková, zooming in on a gold flake whose colors immediately reveal the forces at work.
Gold flakes about 10 micrometers in size are placed in a salt solution, meaning water that contains free ions. When a droplet is added to a gold-coated glass surface, the flakes are drawn toward it, and nanometer-sized cavities (100-200 nanometers) form. This self assembly results from the balance between two forces: the Casimir force, a measurable quantum effect that pulls objects together, and the electrostatic force that arises between charged surfaces in a salt solution.
A halogen lamp shines light into the cavities, where it becomes trapped and reflected. An optical microscope and spectrometer then separate the light into its component wavelengths so the colors can be identified. By adjusting the salt concentration and observing how the flakes shift relative to the surface, researchers can measure the underlying forces. To prevent evaporation, the droplet containing the gold flakes is sealed and covered with a second glass plate.
The platform was developed at Chalmers’ Nanofabrication Laboratory, Myfab Chalmers, and at the Chalmers Materials Analysis Laboratory (CMAL).
For more information: PNAS
Image: Researchers at Chalmers University of Technology, Sweden, have discovered a quick and easy way to study the hidden forces that bind the smallest objects in the universe together. Using gold, salt water, and light, they have created a platform on which the forces can be seen through colors. Two thin glass plates hold everything needed to study nature’s invisible glue. Credit: Chalmers University of Technology | Mia Halleröd Palmgren
