Scientists convince free electrons from gold nanoparticles to behave like those of bulk gold

With a little help from pencil graphite, researchers in Japan have found a way to retain the lustrous colour of bulk gold in gold nanoparticles.

An image depicting the construction strategy of glowing AuNP coating by combining the SILAR method with pencil drawing

Source: © Hiroshi Moriwaki/Shinshu University

Normally gold nanoparticles appear red or blue

Arguably the most captivating property of gold is its glowing golden colour. However, downsizing it to the nanoscale changes its optoelectronic properties via the localised surface plasmon resonance (LSPR) effect, where coherent delocalised electron oscillations are confined at the particle surface. The result is that gold nanoparticles tend to be red or blue, depending on their size. To get the lost golden colour back, the LSPR effect must be suppressed.

A picture showing the fabrication of the controlled glowing of AuNP patterns by pencil drawing

Source: © Hiroshi Moriwaki/Shinshu University

The glowing gold nanoparticle coating can be localised by drawing a line or a pattern with a pencil (a–d). It also works on fabric (e and f)

Researchers led by Hiroshi Moriwaki at Shinshu University have now achieved this with a simple coating method. Moriwaki’s team drew designs using a pencil on cheap substrates like cellulose filter paper. They subsequently embed gold nanoparticles in the pencil graphite deposits using the successive ionic layer adsorption and reaction method. Interactions with the pencil graphite alter the nanoparticles’ properties, changing their colour from red to gold.

The team found that the nanoparticles retain some catalytic activity, and suggest they could also be used in luxury electronics.