Researchers from EPFL, Empa, and CSEM have developed a sustainable smart sensing tag that can be used to signal when shipments of medicines or food have exceeded a safe threshold temperature.

Funded by the Swiss National Science Foundation (SNSF) and Innosuisse as part of the BRIDGE Discovery program, it is the first such tag to be fully compostable.

Vast flows of goods circle the globe every day. They include particularly perishable shipments, such as certain vaccines, medicines and food products. To ensure that these products arrive safely at their destination, they must remain within a certain temperature range throughout the entire supply chain. But it is costly and unsustainable to equip every shipment with silicon-based sensors and wireless chips.

Researchers from EPFL, EMPA, and CSEM have taken up this challenge in a four-year project called GREENsPACK. Together, they have developed a wireless, chipless, printed tag that embeds a non-reversible temperature sensor to detect whether a temperature threshold has been exceeded. The small sticker is silicon-free and made of biodegradable materials.

“Talking about vaccinations, for example, this could mean that the shipment can no longer be used or that the expiry date is invalid,” explains Gustav Nyström, head of Empa’s Cellulose and Wood Materials laboratory, who led the research project.

To do its job, the tag needs neither a battery nor a silicon chip transmitter. Instead, it is based on a wireless electrical resonator made of highly conductive and stable zinc tracks protected by a natural wax.

If these circuits are exposed to an electromagnetic field, for example, from a wireless tag reader, a resonance is created that the reader can decode. If the threshold temperature is exceeded, a solid bio-based oil melts over the circuit, changing this resonance. The next time the label is read, it shows this shipment was once too warm.

Different temperature thresholds can be set depending on the type of oil used, including frozen olive, jojoba and coconut oils, that melt at different temperatures, triggering irreversible resonance frequency shifts. Once melted, the oil is absorbed by a cellulosic material placed underneath, which allows the tag to operate reliably at different inclination angles.

The Soft Transducers Laboratory (LMTS) team in EPFL’s School of Engineering fabricated the sensor on top of a composite substrate of biopolymer and cellulose fibers developed at EMPA, based on a design and readout technology developed at CSEM. The operational system includes a custom-designed reader and software capable of detecting and classifying chipless RFID tags.

“We utilized Principal Component Analysis (PCA) to categorize tags based on their resonant frequency responses, and a dedicated software to manage numerical identifiers”, explains Oleksandr Vorobyov, EM and antennas expert at CSEM.

The GREENsPACK team co-authored a paper describing the device that has recently been published in Nature Communications. In addition, the LMTS team is working on commercializing these findings at recyclable and biodegradable electronics start-up Circelec, a spin-off of EPFL.

“This work represents a green technology platform to make printed circuit boards to reduce electronic waste, which is a major environmental concern: in 2022, the world produced 62 megatons of e-waste – the equivalent of 16 Eiffel towers per day – with only 22% of that properly recycled,” says Danick Briand of LMTS.

Additional information: Nature Communications article

J Bourely, N Fumeaux, X Aeby, J Kim, G Siqueira, C Beyer, D Schmid, O Vorobyov, G Nyström, D Briand: Ecoresorbable chipless temperature-responsive tag made from biodegradable materials for sustainable IoT; Nature Communications (2025)