October 19, 2011 — MIT researchers developed a glass-stamp-based technique that helps fabricate lab-on-chip sensors at a lower cost and in a reproducible, simple manner.
A small, voltage-activated glass stamp etches nanoscale patterns onto metallic surfaces in the lab of Nicholas Fang, associate professor of mechanical engineering. Fang’s engravings act as optical antennae that can identify a single molecule by picking up on its specific wavelength. Controlling the optical antenna dimensions tunes the signals the device reports, Fang says.
The glass stamp technique is an alternative to electron-beam (e-beam) lithography for lab-on-chip fabrication. Fabricating a 6mm2 pattern using e-beam litho typically takes half a day and would price them at $600 each, Fang estimates. Nanoimprint lithography, a low-cost technique where polymer forms a pattern, is imprecise, with bumps and dents in the mold. Makers must use more polymer material to fabricate more copies, as the polymer is washed away during processing.
Fang’s team adopted the nanoimprint lithography approach using glass as a molding material instead of polymer. Molten glass is "very malleable and soft," Fang said, noting that the research was inspired by glassblowers. Fang found that glass easily takes a precise shape at the small-scale. Superionic glass, composed partly of ions, can be electrochemically activated.
The 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. The team then pressed the glass mold onto a flat silver substrate, and applied 90 millivolts above the silver layer. The voltage stimulated ions in both surfaces, and triggered the glass mold to essentially etch into the metal substrate.
 |
| Figure. MIT’s glass stamp reproduces precise, nanometer-scale etchings in silver. The original engraving is 10um wide. Image courtesy of Kyle Jacobs, MIT. |
The group was able to produce patterns of tiny dots, 30nm wide, in various patterns (see the figure) at a resolution more precise than nanoimprint lithography, and that can be reused many times.
While the glass-mold etch process is lower cost, it still requires a master metallic pattern that is formed via expensive lithography. Only one master pattern, and one glass stamp, can be used to mass-produce an entire line of the same sensor.
“With this stamp, I can reproduce maybe tens of hundreds of these sensors, and each of them will be almost identical,” Fang says. “So this is a fascinating advancement to us, and allows us to print more efficient antennae.”
The researchers reported the new fabrication process in the Sept. 21 online edition of the journal Nanotechnology. Access it here: http://iopscience.iop.org/0957-4484/22/42/425301
Learn more at http://web.mit.edu.