Researchers use glass to imprint lab-on-chip sensors
A glass stamp approach similar to nanoimprint lithography and using glass instead of polymer may help researchers clear a large hurdle in scaling up lab-on-a-chip manufacturing.
To fabricate six-mm-square pattern nanosensors using electron-beam lithography typically takes half a day and commercially can run more than $600 apiece, according to the team leader of the new approach.
Nicholas Fang, associate professor of mechanical engineering at the Massachusetts Institute of Technology and his team, has developed an engraving technique that significantly decrease the cost of production by using glass as a molding material.
The technique etches nano-sized patterns on metallic surfaces using a voltage-activated stamp made out of glass. The engravings, made of tiny dots act as optical antennae, can identify a single molecule by its specific wavelength.
“I was inspired by glassblowers, who actually use their skills to form bottles and beakers,” Fang said. “Even though we think of glass as fragile, at the molten stage, it is actually very malleable and soft, and can quickly and smoothly take the shape of a plaster mold. That’s at a large scale, but amazingly it works very well at a small scale too, at very high speed.”
Fang and his team found superionic glass — glass composed partly of ions, which can be electrochemically activated when pumped with voltage — to meet their needs.
The MIT researchers filled a small syringe with glass particles and heated the needle to melt the glass inside. They then pressed the molten glass onto a master pattern, forming a mold that hardened when cooled. Then they pressed the glass mold onto a flat silver substrate, and applied a small, 90-mV electric potential above the silver layer. The voltage stimulated ions in both surfaces, and triggered the glass mold to essentially etch into the metal substrate.
The group was able to produce patterns of 30-nm wide dots in patterns of triangles and rectangles at a resolution more precise than nanoimprint lithography. “You end up with a better cut,” Fang said. “And we have a stamp that can be reused many times.”
Fang said the accepted soft polymer material approach, while inexpensive, can be imprecise with the soft polymer material not fitting exactly around the original pattern, resulting in a mold with bumps, dents and other imperfections — and copies that aren’t exactly the same as the original.
“It [the glass technique] has the potential to be significantly lower cost for patterning metals such as silver. However, a high-throughput process with long stamp life still needs to be demonstrated,” said S.V. Sreenivasan, professor of mechanical engineering at the University of Texas at Austin.