Large flows of goods circle the globe every day. These include particularly sensitive deliveries, such as certain vaccines, medicines and foodstuffs. To ensure that these products arrive safely at their destination, they must remain within a certain temperature and humidity range throughout their entire supply chain. But how do we ensure this? It is costly and unsustainable to equip every single delivery unit with silicon-based sensors and chips. And measurements at nodes in the supply chain say nothing about what has already happened to the sensitive shipment on the way there.

Label measures temperature and relative humidity

Researchers from Empa, EPFL and CSEM have taken up this challenge in a four-year project called "Greenspack". Together, they have developed a smart label that measures the temperature and relative humidity and can "remember" when a certain temperature threshold has been exceeded. The small sticker is not only silicon-free, but also completely biodegradable. The project was funded by the Swiss National Science Foundation (SNSF) and Innosuisse as part of the "BRIDGE Discovery" program. The researchers have published their results in the journal "Nature Communications".

Conductors with memory

To do its job, the smart label needs neither a battery nor a transmitter. Instead, it works in a similar way to an RFID chip. It contains printed tracks made of conductive materials that form circuits with resistive and capacitive elements. If these circuits are exposed to an electromagnetic field, for example by a label reader, a resonance is created that can be deciphered by the reader. The clever thing about this is that the conductivity and capacitance of the individual circuits, and therefore their resonance, change depending on the ambient temperature or humidity. This change provides information about the current temperature and humidity - without any complicated measurement technology.

If the temperature exceeds 25°, a tiny element in one of the conductors melts, irreparably breaking the circuit. The next time the label is read, it will show: This shipment was once too warm. "If we are talking about vaccinations, for example, this could mean that the shipment can no longer be used or that the best-before date is invalid," explains Gustav Nyström, head of Empa's "Cellulose and Wood Materials" laboratory, who led the research project.

This technology relieves the supply chain and reduces its carbon footprint: potentially damaged goods are detected earlier and do not have to be sent on. If the delivery has simply become less durable due to the effect of temperature, it can be redirected to a closer location, for example. "Depending on the materials we use, we can also set the temperature threshold differently," adds Nyström. Labels for frozen goods, for example, would be conceivable.

Biodegradable and sustainable

The researchers' vision is to compost the label at its destination or recycle it into cardboard, as it is completely biodegradable. The Empa researchers have developed their own material for the substrate, which consists of a biopolymer and cellulose fibers. To print the conductive tracks, the Empa and EPFL researchers used a specially developed ink that contains the biodegradable metal zinc. Meanwhile, researchers at CSEM worked on the structure of the label and the readout technology.

Working with biodegradable materials is always a challenge - because they should of course only decompose once their work is done. In addition, the individual components of the label only had to react very selectively to the environmental conditions: "We didn't want the temperature sensor to react to moisture and vice versa," says Nyström. Together, the project partners succeeded in solving the problems. Two EPFL researchers are now working on commercializing the findings from "Greenspack" with a start-up called "Circelec". In future, the Empa researchers led by Gustav Nyström want to delve even deeper into the field of green electronics and explore the potential of smart labels as sensors in agriculture and environmental monitoring.

Original publication:
Bourely, J., Fumeaux, N., Aeby, X., Kim, J., Siqueira, G., Beyer, C., Schmid, D., Vorobyov, O., Nyström, G., & Briand, D. (2025). Ecoresorbable chipless temperature-responsive tag made from biodegradable materials for sustainable IoT. Nature Communications. DOI:10.1038/s41467-025-65458-9

Source: Empa