Did you know that optical sensors made with spider silk could one day help scientists search for trace gases such as ammonia produced by biological processes on Mars?
“The scientists hunting for life on Mars would like to be able to test for small amounts of ammonia,” reports Neil Savage of IEE Spectrum. “[These] might be emitted by the metabolism of microbes, so they need a sensor that can detect that while remaining insensitive to the large amounts of carbon dioxide in the Martian atmosphere.”
Image Credit: Luc Thevanaz/EPFL (via IEEE Spectrum)
Indeed, according to Luc Thévanaz of the Swiss Federal Institute of Technology of Lausanne, conventional optical fibers, currently made of silica glass, are chemically inert, which makes them poorly suited to detect chemicals. This stands in stark contrast to the optical properties of spider silk, which are massively modified by chemicals.
“The presence of certain molecules causes hydrogen bonds in the silk molecules to break and the result is a change in the polarization of light passing through,” Savage explained. “This only works, though, on polar molecules, such as ammonia, which have unequal charges on each end. Non-polar molecules, such as CO2, cause no response.”
Thévanaz and his team have already tested their concept using the silk dragline from a female Nephila edulis spider. Light transmission from visible to infrared was measured up to wavelengths of about 1400 nm. Meanwhile, infrared light at 900m registered optical loss of 4 dB/cm – a measure of how far the light can travel before being absorbed by the material.
Commenting on the above-mentioned story, Patrick Gill, a Principal Research Scientist at Rambus, told us that optical fibers do indeed act as very sensitive environmental probes.
“They can be used to sense motion and vibrations and have even been used to produce optical guitars. In fact, most optical fibers used in telecommunications are made from chemically inactive materials,” Gill noted. “It’s interesting to see Luc Thévanas’ work where he found a material, spider silk, which reversibly interacts with ammonia in a way such that light passing through it is modulated in a way that lets the local ammonia concentration be measured.”
With a variety of different fiber optic chemical materials, says Gill, it should be possible to extract even more information about the chemistry in the local environment.
“This approach could lead to more compact and longer-lasting chemical sensing and monitoring hardware,” he concluded.