Biodegradable microsensors embedded in food for temperature monitoring

Biodegradable microsensors have been developed that could be included within food packaging to check temperature and freshness when on long-haul journeys.

The biocompatible microsensors are created by encapsulating a superfine, tightly wound electrical filament made of magnesium, silicon dioxide and nitride in a compostable polymer.

The magnesium is not poisonous to humans if ingested, while the silicon dioxide and nitride are biocompatible and dissolvable in water. The polymer is produced from corn and potato starch.

“In preparation for transport to Europe, fish from Japan could be fitted with tiny temperature sensors, allowing them to be continuously monitored to ensure they are kept at a cool enough temperature,” said Giovanni Salvatore, a postdoctoral researcher with ETH Zurich.

For use in food packaging, the sensors can’t be a threat to consumer health and need to be small, robust and flexible enough to survive in containers full of fish or other food products.

They are only 16 micrometres thick, making them much thinner than a human hair (100 micrometres), and - being only a few millimetres in length - weigh no more than a fraction of a milligram.

In its current form, the sensor dissolves completely in a one-per-cent saline solution over the course of 67 days.

At present, it continues to function for one day when completely submersed in water, enough time to sufficiently 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,” Salvatore said.

A thicker sensor would be less flexible, however. The current sensor is so thin that it continues to function even if it is completely crumpled or folded. Even when stretched by around 10 per cent of its original size, it remains intact.

For the power supply, researchers have connected the sensor to an external micro battery using ultra-thin, biodegradable zinc cables.

On the same 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 metres.

Producing biocompatible microsensors is currently a very time-consuming and expensive process.

However, Salvatore believes they will soon be able to produce them for the mass market considering recent advances in printing electronic circuits.

“Once the price of biosensors falls enough, they could be used virtually anywhere,” he said.

Sensors would provide the link between the physical and digital world, bringing food products into the “Internet of Things”. Their use would not be limited to temperature measurement either: 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.

He hopes that the battery, processor and transmitter can be integrated into the microsensor by the time they become commonplace.

But more research is required before these components can be used without impacting human health or the environment. The team is therefore currently searching for a biocompatible energy source to power its sensor.

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