Team creates edible temperature sensor for produce
A Swiss team has developed a type of biodegradable microsensor that can record temperature readings. The researchers from ETH Zurich published their findings the journal Advanced Functional Materials.
Manually testing produce that needs to stay at certain temperatures can take significant effort, so constant and wireless monitoring can save time and energy. Currently, RFID and Bluetooth technology allows this but since the sensors are inedible they need to be removed after the products reach their destination.
The end goal of these new sensors is that shippers will put a few of them on randomly selected products and put them in the truck or boat. The actual temperature of the food can then be checked from outside the refrigerated compartment and the sensors won’t need to be retrieved.
Also these sensors are designed to take punishment, be crumpled or stretched, and still function.
The biocompatible microsensors are created by encapsulating a superfine, tightly wound electrical filament made of magnesium, silicon dioxide and nitride in a compostable polymer.
“Magnesium is an important component of our diet, while silicon dioxide and nitride are biocompatible and dissolvable in water,” ETH Zurich wrote in a report. “The polymer in question is produced from corn and potato starch, and its composition complies with EU and U.S. foodstuff legislation.”
The sensor developed by researchers is only 16 micrometers thick, making it much thinner than a human hair (100 micrometers), and – being only a few millimeters in length – weighs no more than a fraction of a milligram. In its current form, the sensor dissolves completely in a one-percent saline solution over the course of 67 days. Currently, the sensor continues to function for one day when completely submersed in water. For example, this time would be sufficient to monitor a shipment of fish from Japan to Europe.
“But it’s relatively easy to extend the operating life by adjusting the thickness of the polymer,” said Giovanni Salvatore, who led the research team.
He said a thicker sensor would be less flexible, however, and that the current sensor is so thin that it continues to function even if it is completely crumpled or when stretched by around 10 percent of its original size.
For the power supply, the researchers connected the sensor to an external micro battery using ultra-thin, biodegradable zinc cables. On the same (non-biodegradable) chip there is a microprocessor and a transmitter that sends the temperature data via Bluetooth to an external computer. This makes it possible to monitor the temperature of a product over a range of 10 to 20 meters.
Applications of the sensor
Currently, producing biodegradable sensors is a very time-consuming and expensive process. However, Salvatore said that soon production costs will drop as the methods of printing electronic circuits becoming increasingly sophisticated.
“Once the price of biosensors falls enough, they could be used virtually anywhere,” Salvatore said.
He sees the sensors as the link between the physical and digital worlds, bringing food products into the “Internet of Things.” Their use would not be limited to temperature measurement either, he said. Similar microsensors could be deployed to monitor pressure, gas build-up and UV exposure.
Salvatore predicts that these biodegradable sensors will be part of our everyday lives within five to 10 years, depending on the level of interest shown by industry. By then, the battery, processor and transmitter could likely be integrated into the microsensor. Considerably more research is still required before these components can be used without concerns for human health, therefore the team is currently searching for a biocompatible energy source to power its sensor.
