Scientists at Chalmers University of Technology in Sweden have created a simple optical platform using gold flakes in salt water to visualize quantum and electrostatic forces at the nanoscale. These forces, described as 'nature's invisible glue,' bind tiny objects and could inform advancements in biosensors, medicines, and even galaxy formation. The technique reveals interactions through colorful light patterns observed under a microscope.
Researchers at Chalmers University of Technology have unveiled a light-based method to observe the subtle forces that govern interactions at the smallest scales. By suspending microscopic gold flakes in a salt solution and placing a drop on a gold-coated glass plate, the flakes are attracted to the surface but halt at nanometer distances, forming tiny cavities that trap light and produce vivid colors like red, green, and gold.
Doctoral student Michaela Hošková, from the Department of Physics, explains the setup: "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."
The platform highlights the balance between the Casimir effect, a quantum force pulling the flakes closer, and the electrostatic repulsion from charged particles in the salt solution. Gold flakes, about 10 micrometers in size, create cavities of 100-200 nanometers, enabling self-assembly. By adjusting salinity and monitoring color shifts via a spectrometer, researchers quantify these forces.
This work builds on four years of research in Professor Timur Shegai's group, evolving from the discovery of self-assembled gold flake resonators. "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," Shegai notes.
Potential applications span physics, chemistry, and materials science, offering insights into particle stability in liquids for medicines, biosensors, water filters, and cosmetics. Hošková adds, "Forces at the nanoscale affect how different materials or structures are assembled... we can gain insights into how the same principles govern nature on much larger scales, even how galaxies form."
The findings appear in the Proceedings of the National Academy of Sciences under the title "Casimir self-assembly: A platform for measuring nanoscale surface interactions in liquids," authored by Hošková, Oleg V. Kotov, Betül Küçüköz, Catherine J. Murphy, and Timur Shegai.