High-performance Wearable Respiratory Sensor Based on Graphene-Oxide-Functionalized Fiber Tip

A compact and high-performance optical fiber sensor for humidity and respiration monitoring was developed based on surface plasmon resonance (SPR) in a multimode-coreless fiber (MCF) tip structure. The probe surface was functionalized with graphene oxide (GO) and Fe₃O₄-Nanoparticle-Doped GO (MGO) using a facile electrostatic layer-by-layer self-assembly technique, which enables the formation of uniform GO/MGO alternate multilayers with high hydrophilicity and surface area. The sensor exhibited a maximum humidity sensitivity of 2.633nm/%RH, a rapid response time of 80 ms, and stable operation over 14 days with a sensitivity variation of less than 5%. The as-fabricated typical Sensor 5 enabled the accurate detection of fast, deep, and normal breathing patterns, with corresponding frequencies of 1.00Hz, 0.16Hz, and 0.49Hz. The respiration monitoring via intensity detection at a fixed wavelength reduces system complexity and cost, demonstrating strong potential for wearable applications in respiratory disease screening, exercise monitoring, and sleep apnea detection.