Smart Mask Delivers Continuous, Battery-Free Breath Monitoring

Collecting stable exhaled breath condensate (EBC) and operating sensors in high humidity limit continuous monitoring. Passive, wearable capture of biomarkers such as metabolites, pathogens, and inflammatory indicators could expand access across diverse patient groups. Researchers now report a battery-free smart mask platform that extends long-term EBC biochemical sensing with materials and system-level upgrades.

Researchers at the California Institute of Technology (Caltech) have developed an updated platform, EBClite, that cools exhaled breath using a hydrogel to condense and collect exhaled breath condensate (EBC) for analysis. Embedded sensors then quantify target biomarkers and wirelessly transmit the data to a phone, tablet, or computer. To address desiccation that previously limited operation to just a few hours, the system incorporates a lithium chloride–infused hydrogel that resists drying and can be rehydrated, enabling reliable multi-day use.

Sensor robustness in the mask’s high-humidity environment was increased by encapsulating the sensing elements in a flexible multilayer material that tolerates repeated dry–wet cycles. The device now operates solely on an ultrathin integrated solar cell, enabling long-term function without recharging or battery replacement. Materials cost is reported at roughly USD 1 per mask.

The team monitored exhaled lactate in healthy volunteers during different physical activities and after carbohydrate intake; lactate levels in breath increased with activity, similar to blood tests, supporting assessments of energy metabolism. EBC collection is entirely passive, making the approach suitable for user-friendly monitoring across many populations, including children, elderly individuals, and critically ill patients.

Collaborators included Johannes Kepler University (Austria) and The Hong Kong University of Science and Technology. The work was published on March 16, 2026, in Nature Sensors. Early deployment efforts with the Gates Foundation are exploring distribution in parts of Africa, and a simplified version is being developed for tuberculosis monitoring.

“We achieved long-term extension of usability through advances in materials science and system-level engineering design. Building on the original mask, these upgrades enable storage and handling practicality, enhance sensing stability, and achieve energy autonomy,” said Wenzheng Heng, postdoctoral scholar research associate in medical engineering at Caltech.

“We can realize battery-free continuous operation during all different types of indoor activities. The solar cell has high-efficiency energy harvesting even in weak light; you don't have to stand under very strong California sunlight for it to work. The entire mask is now very durable and long lasting,” said Wei Gao, professor of medical engineering at Caltech.

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