Scientists at the University of Cambridge are using nanomachines, or extremely tiny robots, to create artificial skin that changes color in the light. Researchers think the skin could be used to create active camouflage or dynamic images.
The material consists of tiny particles of gold coated in a polymer shell which are then squeezed into microscopic droplets of water in oil, according to the research published Tuesday in Advanced Optical Materials. When exposed to heat or light, the particles stick together and the artificial skin's color changes.
The scientists modeled the skin's design after animals like chameleons and cuttlefish, which are able to change color because of chromatophores found in their skin. The color is determined by how close or far apart the particles are. If the nanoparticles spread apart, they show as red. If they're clustered together, they look dark blue. For now, since the researchers have only developed a single layer, the skin can only change to one color. Adding more layers could make the skin more dynamic.
"Loading the nanoparticles into the microdroplets allows us to control the shape and size of the clusters, giving us dramatic color changes," Andrew Salmon, a study co-author, said in a statement.
The idea to try this technique came out of his research group's studies of light's interactions with nanoparticles, which as typically made of gold, Salmon said in an email.
"Recently we developed some gold nanoparticles that can reversibly stick together and then separate again. We spotted that these were changing color far more than we expected. It turns out that when the particles stick together they shadow each other and so end up absorbing far less light than when separated. This is actually how certain animals change color -- cuttlefish for example have skin cells that do this. We realized that by putting the particles into cell-like structures (we used droplets of water) we could enhance the effect," Salmon said.
Salmon noted that the microdroplets are about the width of a human hair. Inside the droplets, the nanoparticles are 14 nanometers across. For reference, a DNA double helix is 2 nanometers across, Salmon said.
"We think it is really amazing that we can start with nanomachines and work our way up to a color-switching skin," he said.