Sensor changes colour depending on pressure levels

The researchers, from the University of California, Riverside, used a self-assembly method to string together gold nanoparticles which they then embedded into a polymer film. These films deformed when pressed, stretching the gold nanoparticle strings by increasing the separation between neighbouring gold nanoparticles. "This increased separation alters the way the nanoparticles interact with light," explained Yadong Yin, an associate professor of chemistry. "When linked together, the gold nanoparticles originally appear blue. But they gradually change to red with increasing pressure as the nanoparticles start disassembling. This easily and visually helps us figure out how much pressure has been applied." The memory sensor that Yin's lab developed differs from commercially available pressure sensor films. The latter indicate pressure by changing the intensity of just one colour (for example, a pale red to a darker red). They also tend to be difficult to interpret and have low resolution and contrast. In contrast, Yin's sensor produces a mosaic of colours and has the benefit of higher contrast and resolution. "The many electronic stress sensors commercially available are bulky and not suitable for certain applications," Yin noted. "For example, it is difficult to tell the stress distribution over a particular area if the contact surfaces are not flat and uniform. Our sensor films can be painted on the contact surfaces so that the colour variance in different areas clearly shows the stress distribution over the contact surface."