Hot off the press: Nanoscale Gutenberg-style printing
Nanopatterns with extremely high resolution are not difficult to produce with todays technology. However, the methods used so far are analogous those used to produce the hand-written books of the era before Gutenberg; they are too slow and work-intensive for commercial fabrication. New nanoprinting techniques offer an interesting solution, says Bach. Along with co-workers, he has developed a process that works with a reusable printing plate.
The printing plate is a silicon waferlike those used for the production of computer chipsthat has been coated with a photoresist and covered with a mask. The wafer is then exposed to an electron beam (electron beam lithography). In the areas exposed to the beam, the photoresist is removed, exposing the wafer for etching. The wafer is then coated with gold. When the photoresist layer is removed, the gold only sticks to the etched areas. Polyethylene glycol chains are then bound specifically to the gold through sulfurhydrogen groups. The chains have positively charged amino groups at their ends. The completed printing plate is then dipped into the ink, a solution of gold nanoparticles coated with negatively charged DNA molecules. Electrostatic attraction causes the DNA to stick to the amino groups, binding the gold nanoparticles to the gold-patterned areas of the printing plate.
The paper is a silicon wafer coated with a whisper-thin gold film and a layer of DNA. These DNA strands are complementary to those on the gold nanoparticles, with which they pair up to form double strands. This type of bond is stronger than the electrostatic attraction between the DNA and the amino groups. When the paper is pressed onto the printing plate and then removed, the gold nanoparticles from the ink remain stuck to the paper in the desired pattern. The printing plate can be cleaned and reused multiple times. Says Bach: Our results demonstrate that it is possible to produce affordable printed elements based on nanoparticles.