Scientists develop gel-based ‘smart tabs’ that detect spoiled food

Smart tag: The green tag on the container shows that the product inside is no longer fresh. Photo credit: Chao Zhang
Smart tag: The green tag on the container shows that the product inside is no longer fresh. Photo credit: Chao Zhang

Scientists in China have come up with a smart tag that tells if foods like milk have gone off, without the need for a stomach-curdling sniff test. Dr. Chao Zhang and a team of researchers from Peking University in Beijing developed a kernel-sized gel-like tab, which attaches to the exterior of product packaging to track the deterioration of food and medicines.

The device, which costs only US $0.002 to make, shows when a product is close to expiration through a red to green color change. The scientist explains why the smart tag won’t leave us looking sour-faced.

Metro: Does this put an end to consumers having to sniff food?

Zhang: It’s an end to sniffing. And since the tag indicates food quality in an indirect and non-destructive manner, you don’t even have to open the container.

Was it the smell of sour milk that encouraged you to create the tag?

Yes, exactly. For example, when I put milk in the trunk of my car and drive home, or forget to put it back into the refrigerator, I do wonder if the temperature is okay. If it’s not, the milk might go sour before the expiration date. The delivery chain with these kind of perishable products is extremely long — manufacturers, transporters, dealers and consumers — which means that we can never know whether or not a product has been exposed to damaging higher temperatures.

When will this technology arrive on the shop floor?

Ah, this is a difficult one for us ‘lab nerds’ to answer. Currently, the only thing we dare to say is that we do not foresee many scientific or technical obstacles in putting this tag into real-world applications. But still, people in the industry world may have concerns over its scientific validity and technical feasibility.

The tag starts off red, then turns green when the food is spoiled. Are you able to adapt the colors at all?

Yes, they can be to some extent. The red-green pairing is because we employed ‘thin’ gold nanorods. If some other metallic nanostructures are used instead, the tag may exhibit some different color spectra. For example, we have found that ‘fat’ gold nanorods go from violet to orange. And if we use flat palladium nanoplates, the color goes from grey to blue.

Would it not be more logical for spoiled food to go from green to red?

We understand that we are used to seeing red as the color of ‘forbidden’ or ‘alert,’ and green as ‘pass’ or ‘safe’ — like with traffic lights. But psychologically, green is the color that human eyes are most sensitive to, which is why we employed green as the color for ‘spoiled.’


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