A paper-thin, fully compostable sensor tag that monitors temperature and humidity without chips, batteries or silicon and even “remembers” if goods were exposed to unsafe heat.
Researchers from Empa, EPFL and CSEM have unveiled a fully biodegradable, chip-free smart sensor tag that monitors temperature and humidity and can permanently signal if safe thresholds were exceeded during shipment. Even as millions of sensitive items from vaccines and medicines to food criss-cross global supply chains daily, keeping them within strict thermal and humidity ranges remains a major challenge. Traditional silicon-based sensors are expensive and unsustainable for mass deployment; moreover, spot checks offer limited insight into conditions experienced en route.
Under the four-year “GREENsPACK” initiative, the team produced a paper-thin, silicon-free sticker that works by printing conductive circuits using a biopolymer and cellulose-fiber substrate, and zinc-based conductive ink. In operation, the tag requires no battery or transmitter: when exposed to an electromagnetic reading field (like an RFID reader), the tag’s circuits resonate differently depending on ambient temperature or humidity allowing remote readout of environmental history.
Critically, the tag also carries a kind of “memory”: if the temperature surpasses a preset threshold (e.g. 25 °C), a small element melts and permanently breaks the circuit. On reading, this shows that the shipment was once exposed to excessive heat, flagging compromised or potentially unsafe goods. After delivery, the tag can simply be composted or recycled with cardboard, since it is fully biodegradable, a significant step toward reducing e-waste in logistics. Initial commercialisation plans are already underway through a spin-out called Circelec.
For electronics-industry readers, this work offers a novel benchmark in “green IoT” and sustainable supply-chain sensors. Combining printed, battery-free electronics with biodegradable materials, this innovation hints at a future where sensitive shipments are tracked in an environmentally friendly, low-cost, high-transparency way avoiding the carbon footprint of silicon chips while preserving traceability and safety.
