High-Aspect-Ratio In2–x Ga x O3 Integrated with Amorphous Al2O3 Nanofibers: All-Inorganic Self-Supporting Wearable Membranes for Ultralow-Concentration NO Sensing in Simulated Exhalation

Achieving high flexibility, breathability, and sensitivity in inorganic semiconductor gas sensors remains a substantial challenge, especially for wearable applications in high-humidity environments. This study develops a hyper-flexible, thermally stable, and highly breathable full-inorganic, self-supporting In2–x Ga x O3–Al2O3/Al2O3 nanofiber membrane sensor, fabricated using a dual-spinneret electrospinning method with an interlocking design. This innovative sensor has a bilayer structure with an amorphous Al2O3 nanofiber substrate layer supporting an active layer of high-aspect-ratio interwoven In2–x Ga x O3 and Al2O3 nanofibers, providing outstanding flexibility, elevated breathability, and strong thermal stability. Owing to low-concentration Ga3+ doping and its nanofiber-built self-supporting porous design, the In1.98Ga0.02O3–Al2O3/Al2O3 sensor demonstrates excellent sensitivity, selectivity, and cycling stability for detecting ultralow-concentration NO biomarker (≈15 ppb) under simulated breath conditions, without performance deterioration, even after 10000 large-angle bending cycles. This work advances the universal fabrication of high-performance, full-inorganic wearable gas sensors for breath-based diagnostic applications.