Chew On This: Edible Silk Sensors To Monitor Your Food

Sick of finding out that your milk is sour only after you’ve taken a big gulp? A new technology will let you simply wave your phone over it—or any food—to get a verdict on whether it’s still edible.

Silk is a marvelously versatile material that is useful in an incredibly wide variety of settings besides luxurious underwear. You can find it in surgical sutures, flexible electronics, and other biologically friendly applications. And soon you might be finding it in your food. Scientists at Tufts University have now engineered the multitalented material into fully chewable food sensors. Pasted onto eggs, stamped onto fruit or floating in milk, they can warn you when your fruit is ripe, or when your milk has gone sour.

"We see a huge market for food," Hu "Tiger" Tao, a postdoc at Tufts University told Co.Exist. "People are always looking forward to some kind of sensor that’s easy to use and gives you information about spoilage."

The flexible sensors are made of gold antennae embedded in a purified silk film support (that Tao and his collaborators first prototyped in 2010). The gold bits are as thin as gold leaf found on some extra-fancy desserts. The silk substrate—made of pure protein—is easily digestible. The whole sensor is flexible, and can curve according to the shape of the fruit it’s being stuck on.

The silk film doubles up as the sensor’s glue, turning sticky when exposed to water. The sensor is then pasted directly onto the food that needs tracking, eliminating the need for an additional glue to keep it clinging on. Tao and his collaborators, led by Fiorenzo Omenetto, tested the sensors on bananas, eggs, apples, cheese, and milk, and published the results in Advanced Materials.

When a fruit ripens or rots, chemical changes churn around inside it. Those changes and differences in the stiffness of the fruit translate to what’s called their dielectric properties. Tao’s gold sensors pick up on that change, and emit a different electromagnetic signal when monitored with a reader. "We can tailor our sensor to be extremely sensitive to the change of the dielectric property," Tao says. Sensors for bananas, for example, are slightly bigger than sensors for milk. The working principles behind the sensors are based on existing RFID tech—the difference here is that the sensors aren’t hard electronics, they’re flexible, edible stickers.

In August last year, Tao was part of a collaboration, headed up by John Rogers at the University of Illinois, that published a paper in Science showing how flexible electronics in the form of an "electronic skin" could stick to the skin and wirelessly track vital health signs. Those weren’t made of silk, but a silk-based approach like those employed on food sensors could also work, says Tao.

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  • Julie Martinez Birmingham

    I hate to tell you nay-sayers, but do a Google search for "anosmia", and you'll find out why something like this could be very helpful. For those of us that are congenital and have never had a sense of smell, being able to see when your food goes bad would be very helpful.

  • Paul

    The perfect device for the compulsive hypochondriac that is constantly in fear of illness. 

  • Gon Arada

    Absolutely unnecessary and Absolutely a waist of both financial and bio resource. Just use your nose and eyes. That said, a deeper look into the chip's functionality and dynamics may unveil further uses/markets.

  • thepseudozombie

    Wow-what-an-amazing-invention and for the human-who-is-not-human-anymore!

  • Spokaloo

    My mom lost her sense of smell due to a medication she was taking - she would love something like this for milk.

  • Julie Martinez Birmingham

    My point exactly. It amazes me how much people that have a sense of smell take it for granted, apparently. I've never had a sense of smell.

  • damionwaters

    This tech doesn't enhance a human trait, it tries to replace one that already works perfectly well. That said, I'm sure there will be a practical application somewhere down the line. 

  • Idontgetit

    The only thing I'm asking myself is ...WHY? I mean ... what about using your nose? Worked for thousands of years. Only good for companies who want to raise food prices ...

  • Julie Martinez Birmingham

    What about those of us that don't have a sense of smell? Don't you think this would be useful?

  • John Wayne

    If you can't tell your tomato is rotten or your milk is spoiled - you need more than just a sensor.

    Besides, who's going to listen to the sensor anyways? If a banana is turning brown on the top does not mean you'll throw it away cause the sensor says it's "spoiled" you might eat the bottom portion that isn't spoiled. 

    Fruits have NATURAL sensors that tell you if they're bad or ripe. 

    Clever idea, but impractical and not worth a penny.

  • tm

    Sometimes the initial application of a technology makes the entire technology seem silly. Reading between the lines, and having had to "sell" my research to grant agencies as a student, this food-sensor may be only one, "practical" application. That's always the question, isn't it? "What's the practical application of your work?"

    Anyway, I look at this and see a budding technology that could ensure the safety and purity of pharmaceuticals delivered to underserved regions. I work in vaccine development and one of the greatest challenges we face is delivering product to where it is most needed (often rural areas without stable refrigeration) while ensuring that it is still viable.

  • tm

    Hundredfire - I completely agree. This sensor, like the current vaccine vial monitors (usually just called 'VVMs' in case you want to get your google on), are not and could not be exposed to the vaccine product. That is, vaccines would almost certainly react with the monitors. Current VVMs are labeled onto the vials/syringes and change color, indicating when the vaccine has been exposed to too much high temperature. They cannot detect low-temperature excursions, which are often more detrimental to the vaccine than higher temperatures.

    So, you can see that even with refrigeration, vaccines can still be susceptible to damage. Power spikes frequently cause freezing of vaccines, rendering them all but inert. Transport to clinics in rural areas (consider Sub-Saharan Africa) is literally sometimes by bicycle. As you suggest, though, there is a lot of effort going into development of sustainable, compact refrigerated containers.

    So, the challenge is to provide viable vaccine (not simply within-expiry) to children in underserved regions. I see a technology like this, see that there's no immediate application there, but keep it in the back of my mind for later. You never know...

  • Hundredfire

    I'm not sure that this technology would be able to detect whether inframicroscopic antigenes have changed their conformation or whatso that could make the vaccines inactive.
    In this particular case, I would rather invest in good compact refrigeration technology than in expiration-indicating sensors

  • tcinphilly

    Why can't they figure out how we can use less energy, or something actually useful instead?

  • Ali

    Even if it doesn't harm us ingesting these sensors, if they become mainstream it would represent an incredible waste of gold, and whatever other elements are required. Considering the entire footprint of the manufacturing and distribution chain, merely so we don't have to look and smell our food and make a reasonable guess, is it really worth it? Sure, if you are extremely susceptible to food poisoning, or for some other medical reason, but surely not the general population.

  • Kellan Vincent

    Stickers that are placed all over fruit these days and are bad environmentally as well. To me the execution is terrific it just needs some refinement and ability to be reused rather than eaten.

  • Brad

    Really? we're that far removed from our natural selves that we need synthetic censors to tell us when a banana is ripe or our milk has gone off.  As genius as the idea may be... this actually makes me a little angry to think that this is the way technology is pushing the human race- away from our natural senses.