Turkeys are called "seven-faced birds" in Japanese for a reason: Their heads can actually change color -- and quite dramatically -- shifting from reds to blues to whites.
The mechanism at play is the swelling or contracting of blood vessels when excited or under duress, which in turn alters the spacing between bundles of collagen fibers that are interspersed throughout the blood vessels, which in turn alters the scattering of light waves and ultimately our perception of the color of a turkey's head.
Bioengineers at UC Berkeley are mimicking this very mechanism to build a biosensor that changes color in the presence of certain chemicals, as well as a companion app that analyzes the color changes to report on which chemicals are present. The idea is to affordably and easily use our smartphones as toxin detectors -- which could prove useful in a variety of settings.
"In our lab, we study how light is generated and changes in nature, and then we use what we learn to engineer novel devices," Seung-Wuk Lee, UC Berkeley associate professor of bioengineering who led the team, said in a school news release. "Our system is convenient, and it is cheap to make...In the future, we could potentially use this same technology to create a breath test to detect cancer and other diseases."
Reporting on their experiments today in the journal Nature Communications, the researchers say they are using a technique they developed a few years ago that enables them to mimic collagen fibers. That work was related to viruses -- they were able to make them behave much like Legos whose shapes could be precisely fine-tuned to perform different functions -- but they also found that the expanding and contracting of tightly bundled nanostructures affected color.
In this work, the team exposed the biosensors to a wide range of volatile organic compounds, from isopropyl alcohol and methane to TNT, and found that even at concentrations of 300 parts per billion, specific color patterns emerged that served as fingerprints to specific chemicals present. They also found that the sensor was sensitive to changes in humidity between 20 and 90 percent, turning redder as humidity rose and bluer as it dropped.
To make the sensor widely available, the researchers also built the iColour Analyser app to demonstrate that smartphones can snap photos of the sensor's color bands and, thanks to the app, translate results for the user.
Lee writes in an e-mail that his team should be able to use the same principle to detect diseases such as lung cancer and diabetes. He says they're already looking for commercial interest in the sensor, and that it will likely take a few years to bring to market.