This Self-Powered Edible Sensor Can Warn You If Your Frozen Food Has Been Thawed and Refrozen

Researchers at the Istituto Italiano di Tecnologia have built a self-powered sensor designed to boost food safety by warning you if frozen food has been previously defrosted — and the sensor itself is edible, too.

"Improper freezing of food causes food waste and negatively impacts the environment," the team explains of its work and the potential for the device it has created. "We propose a device that can detect defrosting events by coupling a temperature-activated galvanic cell with an ionochromic cell, which is activated by the release of ions during current flow. Both the components of the sensor are fabricated through simple and low-energy-consuming procedures from edible materials."

It's the latter that really makes the sensor stand out from the crowd: It's no good putting something in food to keep people safe if the thing itself is dangerous. The sensor the team came up with uses only materials, which are safe to consume: a galvanic cell using electrolytes made from edible salts, tin and gold electrodes, red cabbage juice, and beeswax for structure — culminating in a self-powered device which changes color when frozen food is thawed and then re-frozen.

"The temperature at which the sensor reacts can be tuned between 0 and -50°C [32 and -58°F]," the team explains. "The device can thus be flexibly used in the supply chain: as a sensor, it can measure the length of exposure to above-the-threshold temperatures, while as a detector, it can provide a signal that there was exposure to above-the-threshold temperatures. Such a device can ensure that frozen food is handled correctly and is safe for consumption. As a sensor, it could be used by the workers in the supply chain, while as a detector, it could be useful for end consumers, ensuring that the food was properly frozen during the whole supply chain."

The researchers describe their creation as "a proof of concept" for edible sensors, while admitting that the size of the electrodes in the prototype make it poor eating — suggesting that miniaturization through thin-film metal printing and an optimized design will take care of that problem. "This sensor," the team concludes, "could pave the way for an inexpensive and safe technology to be largely exploited in the food and drug cold supply chains, reducing wastes and improving safety."

The team's work is published under open-access terms in the journal ACS Sensors.