Gold Can Now Produce Colours. New Study Explains How

Gold nanocylinders are suspended in a gel as part of this technique. The colour transmitted by the gel depends on the orientation of the gold nanocylinders.

"There is a pot of gold at the end of the rainbow," folk belief says. However, a new technology is now turning that idea on its head. The technique is using particles of gold to produce colours. The method developed at Aalto University in Finland could indicate a new display technology. 

The study describing the interesting technique was recently published in the journal Advanced Functional Materials.

How Can Gold Produce Colours?

Gold nanocylinders are suspended in a gel as part of this technique. The gel transmits certain colours when it is lit by polarised light, which is light that is reflected from or transmitted through a single plane so that all its vibrations are restricted to a single plane. The colour transmitted by the gel depends on the orientation of the gold nanocylinders, the study said.

The study team used DNA molecules to control the orientation of gold nanocylinders in the gel. 

In a statement released by Aalto University, Joonas Ryssy, the lead author on the paper, said DNA is not just an information carrier, but can also be a building block. The researchers designed the DNA molecules to have a certain melting temperature, so they could program the material. 

The DNA molecules behave in different ways depending on whether the gel temperature is increased or decreased. When the gel heats up past its melting temperature, the DNA molecules loosen their grip, and the gold nanocylinders change their orientation, the study said. Meanwhile, when the temperature drops, the DNA molecules tighten up again, and the nanoparticles go back to their original position. 

The scientists tested several custom DNA molecules with different melting temperatures to find the best response. The technology can produce red and green light using the current system. Further work can make blue light transmission possible. Then, this approach could be used to generate any colour by mixing red, green, and blue.

Colours Can Be Generated In A Dynamic And Reversible Way

Sesha Manuguri, a researcher at Aalto University who led the study, said the whole concept is to use simple methods, simple materials and simple tools to generate colours in a dynamic and reversible way. 

According to Manuguri, part of the elegance of the technique is that the gold nanocylinders accomplish both the necessary tasks. He said the gold nanorods get hot when they are lit, heating the gel, and they are also responsible for colour formation. Therefore, one does not need separate heating elements. 

The approach could be used to produce colour in different kinds of displays, with further development. The materials are biocompatible, and hence, could be ideal for displays on wearable sensor devices. The technology could also be used in billboards or other displays, the study said.

Manuguri added that the researchers have done the basic science to bring these building blocks together in a symbiotic manner to create something functional. Engineers can further explore what kind of devices could be made, he added.