HC-ARF-based FERS gas sensors. (a) FERS setup for detecting key gases generated during the thermal runaway of lithium-ion batteries (reproduced from Ref. [112]). (b–d) FERS sensor for CO₂ isotope detection [113]: (b) experimental setup (inset: 3D model and microscope image of the HC-ARF cross section); (c) schematic illustration of the spatial filtering process; (d) comparison of Raman signals (left) without and (right) with spatial filtering.