Want a ‘Shrinky Dinks’ approach to nano-sized devices? Try hydrogels

Rather than making devices small to begin with, start big and make them small later

tiny animals from the Chinese zodiac, made in hydrogels of different colors. Top row from left: purple monkey, yellow and purple pig, yellow and purple snake, bluish gray dog, green rabbit. Bottom row from left: green tiger, yellow goat, orange horse, purple rooster, teal rat.

These Chinese zodiac animals etched in hydrogels come in many materials, including gold (goat), titanium dioxide (snake) and luminescent nanoparticles (rabbit). The images on the bottom are each a few dozen micrometers wide. The images at the top started that big and were then shrunk to roughly one-tenth their size.

The Chinese University of Hong Kong, Carnegie Mellon University

High-tech shrink art may be the key to making tiny electronics, 3-D nanostructures or even holograms for hiding secret messages.

A new approach to making tiny structures relies on shrinking them down after building them, rather than making them small to begin with, researchers report in the Dec. 23 Science.

The key is spongelike hydrogel materials that expand or contract in response to surrounding chemicals (SN: 1/20/10). By inscribing patterns in hydrogels with a laser and then shrinking the gels down to about one-thirteenth their original size, the researchers created patterns with details as small as 25 billionths of a meter across.

At that level of precision, the researchers could create letters small enough to easily write this entire article along the circumference of a typical human hair.

Biological scientist Yongxin Zhao and colleagues deposited a variety of materials in the patterns to create nanoscopic images of Chinese zodiac animals. By shrinking the hydrogels after laser etching, several of the images ended up roughly the size of a red blood cell. They included a monkey made of silver, a gold-silver alloy pig, a titanium dioxide snake, an iron oxide dog and a rabbit made of luminescent nanoparticles.

two red dragons made from hydrogels
These two dragons, each roughly 40 micrometers long, were made by depositing cadmium selenide quantum dots onto a laser-etched hydrogel. The red stripes on the left dragon are each just 200 nanometers thick.The Chinese University of Hong Kong, Carnegie Mellon University

Because the hydrogels can be repeatedly shrunk and expanded with chemical baths, the researchers were also able to create holograms in layers inside a chunk of hydrogel to encode secret information. Shrinking a hydrogel hologram makes it unreadable. “If you want to read it, you have to expand the sample,” says Zhao, of Carnegie Mellon University in Pittsburgh. “But you need to expand it to exactly the same extent” as the original. In effect, knowing how much to expand the hydrogel serves as a key to unlock the information hidden inside.  

But the most exciting aspect of the research, Zhao says, is the wide range of materials that researchers can use on such minute scales. “We will be able to combine different types of materials together and make truly functional nanodevices.”

James Riordon is a freelance science writer who covers physics, math, astronomy and occasional lifestyle stories.

More Stories from Science News on Materials Science

From the Nature Index

Paid Content