Silk and Gold Device Could Serve As Implantable Biosensor
Silk-based metamaterial photographed on a background of silk fibers. The tiny, flexible devices can be rolled into capsule-like shapes.
CREDIT: Hu Tao, Tufts University
By combining the bio-compatible quality of silk with the radio broadcast ability of gold, scientists have created an implantable transmitter that could remotely alert doctors about changes in a patient's medical condition.
The silk and gold device belongs to a class of compounds called metamaterials, which respond to electromagnetic waves in ways that atoms in natural materials do not.
Researchers from Tufts University and Boston University focused on metamaterial silk composites that are resonant at the terahertz frequency. This is the frequency where many chemical and biological agents show unique "fingerprints," which could potentially be used for biosensing.
The silk is "a very peculiar kind of antenna - actually, a lot of small antennas that behave as one," said Fiorenzo Omenetto, a professor of Biomedical Engineering at Tufts. "The silk metamaterial composite is sensitive to the dieletric properties of the silk substrate and can monitor the interaction between the silk and the local environment. For example, the metamaterial might signal changes in a bioreactive silk substrate that has been doped with proteins or enzymes."
The researchers sprayed gold-based metamaterial structures directly on pre-made silk films with micro-fabricated stencils using a shadow mask evaporation technique. Spraying the metamaterial onto the flexible silk films created a composite so pliable that it could be wrapped into small, capsule-like cylinders.
Silk films are highly transparent at certain frequencies, so metamaterial silk composites display a strong resonant electromagnetic response. Each fabricated sample was 1 square centimeter (0.115 square inches) and contained 10,000 metamaterial resonators with unique resonant response at the desired frequencies.