Shrinking hydrogels: a big idea for nanodevices
Researchers have developed a way to shrink printable nanodevices to as thin as 10s of nanometers, by creating the 3D pattern of a material in hydrogel and reducing it for nanoscale resolution.
Three years ago, when Professor Chen Shih-chi was visiting Carnegie Mellon University as an invited speaker from Hong Kong, he happened to strike up a conversation with Dr Leon Zhao Yongxin. As a result of their discussion, the two researchers became inspired to use their combined expertise to solve a long-standing challenge in the manufacture of nanodevices.
Chen is a professor in the Department of Mechanical and Automation Engineering at the Chinese University of Hong Kong. At Carnegie Mellon, Zhao’s Biophotonics Lab develops technique to study biological and pathological processes in cells and tissues. For example, expansion microscopy is a protocol that enlarges samples embedded in a hydrogel, enabling a view of fine details without any upgrade of existing microscopes. What Chen and Zhao wanted to do was the exact opposite: create the 3D pattern of a material in hydrogel and shrink it for nanoscale resolution.
“Shih-chi is known for inventing the ultrafast two-photon lithography system,” Zhao said. “We met during his visit to Carnegie Mellon and decided to combine our techniques and expertise to pursue this radical idea.”
Conventional 3D nanoscale printers focus a laser point to process materials serially, which is why it takes a long time to complete a design. Chen’s invention changes the width of the laser’s pulse to form patterned light sheets, allowing for a whole image containing hundreds of thousands of pixels to be printed at once. Called ‘femtosecond project two-photon lithography’, the method is up to 1,000 times faster than previous nanoprinting techniques.
For the process, researchers would direct the femtosecond two-photon laser to modify the network structure and pore size of the hydrogel, which then creates boundaries for water-dispersible materials. The hydrogel would then be immersed in water containing nanoparticles of metal, alloys, diamond, molecular crystals, polymers or fountain pen ink.
“Through fortuitous happenstance, the nanomaterials we tried were all attracted automatically to the printed pattern in hydrogel and assembled beautifully,” Zhao said. “As the gel shrinks and dehydrates, the materials become even more densely packed and connect to each other.”
This collaboration between Chen and Zhao may open doors for designing sophisticated nanodevices. The results have been published in the journal Science.
Zhao said: "In the end we would like to use the new technology to fabricate functional nanodevices, like nanocircuits, nanobiosensors, or even nanorobots for different applications. We are only limited by our imagination."