Nanostructures can be generated from silk in an environmentally friendly process, Tufts University engineers have shown. The engineers used water as a developing agent and standard fabrication techniques to demonstrate the concept.
The approach gives a green alternative to the commonly used toxic materials in nanofabrication, and delivers fabrication quality comparable to conventional synthetic polymers for the manufacture of semi-conductors and other electronic and photonic devices.
Nanofabrication uses high-resolution patterning involving features so small that they have at least one dimension no larger than 100 nanometers, the size of particles filtered out by surgical masks.
Nanofabrication Polymer Development
Nanoscale fabrication is usually obtained depositing thin films of customized polymers, known as resists, onto silicon wafers. Each resist layer is consecutively patterned by using light or electrons, by electron beam lithography, to expose the part of the resist not covered by a mask.
Next, positive resists are dissolved when subjected to a developer while negative resists remain behind after development. The composition and configuration of the layers establish the properties of the structure.
But developing the resists typically necessitates use of toxic solvent chemicals, which need careful, and costly, handling and disposal. Important advances have been made using green resists that can be developed with water, but these techniques do not have the needed precision or scalability.
Biologically Active Silk Sensors
In this work, the Tufts engineers fabricated nanoscale photonic lattices using both neat silk and functionalized silk doped with quantum dots, green fluorescent proteins (GFPs) or horseradish peroxidase (HRP).
Sunghwan Kim, Benedetto Marelli, Mark A. Brenckle, Alexander N. Mitropoulos, Eun-Seok Gil, Konstantinos Tsioris, Hu Tao, David L. Kaplan, Fiorenzo G. Omenetto. All-water-based electron-beam lithography using silk as a resist. Nature Nanotechnology, 2014; DOI: 10.1038/nnano.2014.47
Tao, H., Kaplan, D. L. & Omenetto, F. G. Silk materials—a road to sustainable high technology. Adv. Mater. 24, 2824–2837 (2012).
Image courtesy of Tufts University