Master the art of nanoscale construction to breathe easily and thwart fraud

Special anti-counterfeiting and chemical detection tools that we can use with our eyes could be created thanks to a new method of construction at the nanoscale.

In a world first, researchers at the ARC Center of Excellence in Exciton Science were able to arrange tiny gold rods in exact patterns and in large enough numbers for practical use. The results were published in the journal Advanced functional materials.

Importantly, these gold rods can be arranged to generate a variety of colors, which change depending on how they are displayed.

This makes them a great anti-counterfeiting feature. For example, when used on a banknote or passport, they could be useful for cashiers or customs agents.

They can also be modified to transform different colors in the presence of chemicals, acting as a warning for dangerous levels of carbon monoxide and other gases.

Although these effects have been observed previously, it has not been possible to render them in a dimension visible to the naked eye. A new approach to chemical assembly was needed.

Consider this: Getting bricks in a house to match is quite simple. Go a little smaller and kids can do the same with Lego. But how do you build things with nano-scale precision?

A nanometer is about one billionth of the size of a meter. To put things in perspective, a sheet of paper is about 100,000 nanometers thick and nails grow about a nanometer every second. So unless you’re Ant Man and can shrink down to the subatomic level, that’s a tough task.

But luckily, you don’t need to be an Avenger to get the job done. Lead author Heyou Zhang, a Ph.D. candidate at the University of Melbourne, used a technique called electrophoretic deposition (EPD).

“The idea of ​​my PhD is to be able to better control individual nanoparticles. Builders build houses, brick by brick, and they can put any brick wherever they want,” Heyou said.

“I want to use nanoparticles in a similar way. But at the nanoscale, you can’t move the nanoparticles by yourself. They’re invisible. You have to use some method to guide or push the particle into a certain position.”

EPD involves applying an electric field of a certain intensity to the materials and using the separation of positive and negative charges to push the rods into place.

Heyou explained: “You have a positive potential, and if the particle is negative, they attract each other. If I have the positive potential on the side of a wall and I have holes in the wall, the particle can only be attracted to those holes.”

With the technique, Heyou and his colleagues are able to build collections of more than one million nanotubes per square millimeter, according to models of their choice.

In addition to anti-counterfeiting and chemical detection, the assembly method could have applications in renewable energy, smartphones, laptops and efficient lighting.

Provided by ARC Center of Excellence in Exciton Science