Surface-engineered boron carbide nanostructures for non-contact respiratory monitoring

Accurate and continuous monitoring of breathing patterns is crucial for the early detection and effective management of respiratory conditions, including asthma, chronic obstructive pulmonary disease (COPD), and sleep apnea. In this work, we introduce a novel nanostructured boron carbide (B₄C)-based non-invasive, highly responsive humidity sensor for real-time breath detection. The fabrication of the interdigitated electrode (IDE) of the sensor is performed using a standard photolithography approach and on it the sensor material B₄C nanostructures are drop-cast for humidity sensing. The sensing device responds to current variations during breathing cycles, showing a rapid response time of ∼0.5 s and a recovery time of ∼0.7 s with an operating range of 8.5% RH to 91% RH. The various breathing patterns - such as normal, shallow, rapid, and apnea-like respiration - were detected accurately without requiring physical contact or calibration. This sensing performance is attributed to the atomic-scale surface interactions between B₄C and biomarkers, which enable rapid proton transport, attract vapour molecules of water and others. The mechanism arises from the synergistic interactions of vapour molecules or markers within multi-adsorption layers on the surface-engineered, chemically stable, and oxidation-resistant B₄C nanostructures. This study highlights boron carbide as a versatile and scalable material for humidity-based breath sensing, offering a cost-effective, room-temperature platform for wearable and clinical respiratory monitoring applications.