Silky sensor: A biosensor made from silk and gold can pick up tiny signals from proteins and chemicals in the body. Researchers patterned gold over a silk film and wrapped it into a capsule shape to form a small antenna.   Credit: Hu “Tiger” Tao



MIT Technology Review, August 24, 2010, by Jennifer Chu

  A prototype silk biosensor could someday alert doctors to signs of disease.

Silk and gold, usually a pairing for the runways of Milan, are now the main ingredients for a new kind of implantable biosensor. Researchers at Tufts University have crafted a small antenna from liquid silk and micropatterned gold. The antenna is designed to spot specific proteins and chemicals in the body, and alert doctors wirelessly to signs of disease. Scientists say the implant could someday help patients with diabetes track their glucose levels without having to test themselves daily.

According to Fiorenzo Omenetto, professor of biomedical engineering at Tufts University, silk is a natural platform for medical implants–it’s biocompatible, and while it’s delicate and pliable, it’s also tougher than Kevlar. Implanted in the body, silk can conform to any tissue surface, and, unlike conventional polymer-based implants, it could stay in place over a long period of time without adverse effects. Omenetto has previously taken advantage of these properties to mold silk into tiny chips and flexible meshes, pairing the material with transistors to track molecules, and with electrodes to monitor brain activity.

Now Omenetto is exploring the combination of silk and metamaterials–metals like gold, copper, and silver manipulated at the micro- and nanoscale to exhibit electromagnetic characteristics not normally found in nature. For example, scientists have created metamaterials that act as “invisibility cloaks” by manipulating metals to bend light all the way around an object, rendering it invisible.

Omenetto and his colleague Richard Averitt, associate professor of physics at Boston University, used similar principles to create a metamaterial that’s responsive not to visible light, but rather to frequencies further down the electromagnetic spectrum, within the terahertz range. Not coincidentally, proteins, enzymes, and chemicals in the body are naturally resonant at terahertz frequencies, and, according to Averitt, each biological agent has its own terahertz “signature.”

Terahertz science is a new and growing field, and several research groups are investigating specific protein “T-ray” signatures. A silk metamaterial antenna could someday pick up these specific signals and then send a wireless signal to a computer, to report on chemical levels and monitor disease.

To engineer the responsive end of such an antenna, the team first created a biocompatible base by boiling down silk and pouring the liquid solution into a centimeter-square film. The researchers then sprayed gold onto the silk film, using tiny stencils to create different patterns all along the film. Each area of the film responds to a different terahertz frequency depending on the shape of the gold pattern. The team then wrapped the patterned film around a capsule to form an antenna.

To test its performance, Omenetto and Averitt subjected the antenna to terahertz radiation and found that the antenna was resonant at specific frequencies. Going a step further, the researchers implanted the antenna in several layers of muscle tissue from a pig, and still detected a terahertz signal.

“We’ll try to sense something next and maybe put the antenna in contact with something we’d like to detect, like glucose,” says Omenetto. “We’ll see if we can replicate a proof of principle, and try to add some meaning to the resonance.”

Rajesh Naik, a materials science expert at the Air Force Research Laboratory at Wright-Patterson Air Force Base, says the research has great practical potential.

“Proteins and other molecules can be entrapped within silk films, allowing one to monitor in-vivo chemical reactions,” says Naik. “Similar resonating structures can be patterned onto other polymeric materials, but silk has an added advantage of being biocompatible.”, August 24, 2010, by Andy Greenberg  —  As the privacy controversy around full-body security scans begins to simmer, it’s worth noting that courthouses and airport security checkpoints aren’t the only places where backscatter x-ray vision is being deployed. The same technology, capable of seeing through clothes and walls, has also been rolling out on U.S. streets.

American Science & Engineering, a company based in Billerica, Massachusetts, has sold U.S. and foreign government agencies more than 500 backscatter x-ray scanners mounted in vans that can be driven past neighboring vehicles to see their contents, Joe Reiss, a vice president of marketing at the company told me in an interview. While the biggest buyer of AS&E’s machines over the last seven years has been the Department of Defense operations in Afghanistan and Iraq, Reiss says law enforcement agencies have also deployed the vans to search for vehicle-based bombs in the U.S.

“This product is now the largest selling cargo and vehicle inspection system ever,” says Reiss.

Here’s a video of the vans in action.

The Z Backscatter Vans, or ZBVs, as the company calls them, bounce a narrow stream of x-rays off and through nearby objects, and read which ones come back. Absorbed rays indicate dense material such as steel. Scattered rays indicate less-dense objects that can include explosives, drugs, or human bodies. That capability makes them powerful tools for security, law enforcement, and border control.

It would also seem to make the vans mobile versions of the same scanning technique that’s riled privacy advocates as it’s been deployed in airports around the country. The Electronic Privacy Information Center (EPIC) is currently suing the DHS to stop airport deployments of the backscatter scanners, which can reveal detailed images of human bodies. (Just how much detail became clear last May, when TSA employee Rolando Negrin was charged with assaulting a coworker who made jokes about the size of Negrin’s genitalia after Negrin received a full-body scan.)

“It’s no surprise that goverments and vendors are very enthusiastic about [the vans],” says Marc Rotenberg, executive director of EPIC. “But from a privacy perspective, it’s one of the most intrusive technologies conceivable.”

AS&E’s Reiss counters privacy critics by pointing out that the ZBV scans don’t capture nearly as much detail of human bodies as their airport counterparts. The company’s marketing materials say that its “primary purpose is to image vehicles and their contents,” and that “the system cannot be used to identify an individual, or the race, sex or age of the person.”

Though Reiss admits that the systems “to a large degree will penetrate clothing,” he points to the lack of features in images of humans like the one shown at right, far less detail than is obtained from the airport scans. “From a privacy standpoint, I’m hard-pressed to see what the concern or objection could be,” he says.

But EPIC’s Rotenberg says that the scans, like those in the airport, potentially violate the fourth amendment. “Without a warrant, the government doesn’t have a right to peer beneath your clothes without probable cause,” he says. Even airport scans are typically used only as a secondary security measure, he points out. “If the scans can only be used in exceptional cases in airports, the idea that they can be used routinely on city streets is a very hard argument to make.”

The TSA’s official policy dictates that full-body scans must be viewed in a separate room from any guards dealing directly with subjects of the scans, and that the scanners won’t save any images. Just what sort of safeguards might be in place for AS&E’s scanning vans isn’t clear, given that the company won’t reveal just which law enforcement agencies, organizations within the DHS, or foreign governments have purchased the equipment. Reiss says AS&E has customers on “all continents except Antarctica.”

Reiss adds that the vans do have the capability of storing images. “Sometimes customers need to save images for evidentiary reasons,” he says. “We do what our customers need.”