myIn 1897, British author H.G. Wells published his most famous novel, The invisible manThe main character invents a serum to make his body transparent. The principle is simple: control the refractive index of his cells to bring it closer to that of air. Thus, light rays pass through different environments without detecting the slightest boundary. And Griffin becomes invisible. Pure science fiction, of course.
However, it is based on the same theory that an American team has just developed a method to make a mouse partially transparent. Coming from two laboratories at Stanford University, it announces in an article published on September 5 in the journal ScienceHe was able to see through the skin of rodents thanks to the local application of a simple dye.
You probably don’t know tartrazine. But you’ve been swallowing it for a long time. The orange-yellow in soft drinks, candy, or even chips and tacos is what it is, hidden under the code name E102. California researchers observed that when they brushed the fur of a previously shaved mouse, it took on a red tint, as expected, but also became transparent.
This “apparent magic trick”As described by physicist Zihao Ou, first author of the paper, a postdoctoral fellow at Stanford during the research and now a professor at the University of Texas at Dallas, it picks up on Wells’s idea. “The skin is a complex mixture of water – with a low refractive index – and lipids and proteins – with a high refractive index”explains. Remember that the refractive index measures the ability of a medium to slow down or deflect a ray of light. Depending on whether a ray hits water or lipids and proteins, it takes a different direction. Like a thick fog (air and water) or a mixture of water and oil, it is impossible to see through it. “By adding the dye, the aqueous medium sees its refractive index increase until it approaches that of lipids and proteins”the researcher continues. And that’s all.
A spectacular and reversible operation
So much so that we arrived at the counterintuitive result that, in order to obtain transparency, the researchers reduced the diffusion of light in the water. A bit like adding ink to water to make it clearer… “Until now we had tried to do the opposite, purify the water by removing lipids.explains Alain Chédotal, a researcher at the Paris Vision Institute, who has developed methods for studying embryos using transparency. But it only worked on sampled tissue. What they offer is very original and very simple. »
You have 37.85% of this article left to read. The rest is reserved for subscribers.
