A new generation of microsensors may be the missing link between food products and the Internet of Things. Researchers at EHT Zurich have developed an ultra-thin temperature sensor that is both bio-compatible and biodegradable.
Microsensors are already used in many different applications, such as toxic gas detection. They are also integrated into miniature transmitter-receiver systems, such as RFID chips. But because the sensors often contain precious metals that are harmful to the environment and human health, they are not suitable for medical applications involving direct contact with the body or for use in food products. There is therefore much interest, both in science and industry, in developing microsensors made of non-toxic materials that are also biodegradable.
Polymer
A team of scientists from several ETH institutes worked together to develop a microsensor that does have these properties. The sensor's tightly wound electrical filament is made of magnesium, silicon dioxide and nitride and encapsulated in a compostable polymer. Magnesium is an important part of our diet, while silicon dioxide and nitride are biocompatible and dissolve in water. The polymer in question is made from corn and potato starch and meets the requirements of food legislation in both the EU and the US.
Giovanni Salvatore, one of the researchers involved, is convinced that these biodegradable microsensors are the future. To illustrate this, he cites one key application as an example. 'When fish are transported from Japan to the Netherlands, they can be fitted with ultra-small temperature sensors, making it possible to continuously monitor the fish to make sure the temperature stays low enough.' This requires sensors that are suitable for use in food and do not pose a health hazard. The sensors must also be small, robust and flexible enough to survive in containers full of fish and other food products.
Ultrathin
That the microsensors developed at the ETH are thin enough is obvious. The sensor is only 16 micrometres (µm) thick, which is about five times thinner than a human hair, which is 100 micrometres thick. The sensor is also only a few millimetres long and weighs less than a fraction of a milligram. In its current form, the sensor completely dissolves in a 1% salt solution within 67 days, remaining functional for another day when fully immersed in water. That's enough time to monitor a ship cargo from Japan to Europe. 'But it is relatively easy to extend the lifetime by adjusting the thickness of the polymer,' says Salvatore. However, a thick sensor would again be less flexible. The current sensor is so thin that it retains its performance even if it is completely crumpled or folded. Even if it is stretched to 10% of its original size, the sensor remains intact.
For power, the scientists connected the sensor to an external micro-battery using ultra-thin, biodegradable zinc cables. On the same (non-biodegradable) chip is a microprocessor and a transmitter that sends temperature data to an external computer via Bluetooth. That makes it possible to monitor the temperature of a product from a distance of 10 to 20 metres.
Internet of Things
Producing biocompatible microsensors is currently a time-consuming and costly process. The ETH researchers believe that it will soon become possible to produce such sensors on a large scale, especially if the methods for printing electronic circuits are refined. 'Once the price of biosensors is low enough, they can be used virtually anywhere.' They then also form a link between the physical and digital worlds, making food part of Internet of Things as well.
The researchers expect bio-microsensors like the one they have developed to become part of our daily lives in the future. The battery, processor and transmitter will then probably be integrated into the sensor itself.
By: Kelly Bakker
Source: ETH + The Factory Files
Photo: YouTube ETH Zurich
