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

The art of high tech could be the key to making tiny electronics, 3-D nanostructures or even holograms to hide secret messages.

A new approach to making tiny structures tries to refuse to build them after they are built, rather than making them small in the first place, researchers report on Dec. 23. Science.

The key is a spongelike hydrogel material that expands or contracts in response to the surrounding environment (SN: 1/20/10). By inscribing patterns on hydrogels with a laser and shrinking the gels to about one-thirteenth their original size, the researchers created patterns with details less than twenty billionths of a meter across.

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

Biological scientist Yongxin Zhao and colleagues deposited various materials on samples to create nanoscopic images of Chinese zodiac animals. By shrinking the hydrogel after laser etching, several red blood cell-sized images are roughly finished. A silver monkey, a tin silver pig, a titanium dioxide snake, an iron oxide dog and a shiny rabbit made of nanoparticles.

Because hydrogels can often crack and expand with chemical baths, researchers can also create holograms in the layers inside a piece of hydrogel to encode secret information. The shrinking hydrogel renders the hologram unreadable. “If you want to read, you have to expand your sample,” says Zhao, of Carnegie Mellon University in Pittsburgh. “But we need to expand exactly the same” as the original. In fact, knowing how much a hydrogel can expand is the key to unlocking the information hidden inside.

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