What holds matter together at the tiniest scales? Scientists have long known that unseen forces — sometimes called “nature’s invisible glue” — govern how particles interact, but observing them in action has been extremely difficult. Now, researchers at Chalmers University of Technology in Sweden have developed a simple yet powerful way to visualize these forces using gold flakes, salt water, and light.

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Seeing the Invisible

In a bright physics lab, doctoral student Michaela Hošková demonstrates the technique. Millions of microscopic gold flakes are suspended in a salt solution. A single drop is placed on a gold-coated glass plate under an optical microscope. Almost instantly, the flakes are drawn toward the surface — but they don’t touch it.

These tiny gaps, only hundreds of nanometers wide, trap light, producing shimmering colors that shift between red, green, and gold. The colors are not just beautiful; they reveal the hidden forces at play between the flakes and the substrate.

“Through these nanoscopic cavities, we can observe how fundamental forces in nature interact without interfering,” Hošková explains. “It’s a simple way to study something that has been invisible for so long.”

The Science Behind the Colors

Two forces compete to create this delicate balance. The Casimir force, a quantum effect, pulls the flakes closer to the surface. Meanwhile, electrostatic forces from the charged ions in the salt solution push them apart. When these forces balance perfectly, self-assembly occurs, forming the nanometer-scale cavities that trap light.

By varying the salt concentration and observing the flakes’ behavior, researchers can measure and analyze the fundamental forces with remarkable precision.

From Nanoscience to the Cosmos

This new platform is not only a breakthrough for understanding tiny particles; it has broad implications across science. Insights from these experiments could improve the design of biosensors, water filters, and medical delivery systems, or even help explain how larger structures, like galaxies, form in the universe.

“Understanding forces at the nanoscale gives us clues about how nature organizes itself at every level,” says Professor Timur Shegai, lead researcher. “From tiny particles to large-scale systems, the same principles are at work.”

Gold Flakes as Floating Sensors

The team’s platform is incredibly versatile. The self-assembling gold flakes act as floating sensors, allowing scientists to study individual particle interactions that were previously impossible to observe directly. Unlike other methods that require expensive, complex instruments, this approach is fast, simple, and visually striking.

“The beauty of this method is its simplicity,” Hošková says. “We don’t have to manipulate the flakes — their natural movements and interactions reveal everything we need to see.”

Future Applications

This innovative platform could impact multiple fields, from materials science and chemistry to medicine and nanotechnology. By understanding how particles interact in liquids, scientists could design more stable formulations for cosmetics, develop more precise drug delivery systems, or even engineer new materials that assemble themselves automatically.

The study, titled “Casimir Self-Assembly: A Platform for Measuring Nanoscale Surface Interactions in Liquids,” was published in PNAS (Proceedings of the National Academy of Sciences). The research team includes Michaela Hošková, Oleg V. Kotov, Betül Küçüköz, Timur Shegai from Chalmers University, and Catherine J. Murphy from the University of Illinois.

With just a drop of gold flakes in salt water, scientists can now observe nature’s invisible forces in action. This simple yet powerful method opens doors to discoveries in physics, chemistry, biology, and even astronomy. By turning the invisible into something visible, Chalmers researchers have given us a new way to understand the very forces that hold our world — and the universe — together.