Synergistic enhancement of ammonia sensing using U-shaped tapered no-core fiber and functional group-modulated MXene

• A novel NH 3 sensor based on MXene-functionalized U-shaped Tapered No-core Fiber. • High sensitivity of 1.8 pm/ppm and good linearity achieved for NH 3 detection. • DFT reveals sensing mechanism: charge transfer alters MXene’s refractive index. • A combined theoretical and experimental strategy for designing optical gas sensors. The development of high-sensitivity sensing technologies for ammonia (NH 3 ), a common and toxic industrial gas, is crucial for public safety and environmental protection. Two-dimensional materials MXene have shown great potential in gas sensing due to their excellent electronic and optical properties, yet their integration with fiber-optic platforms and the underlying sensing mechanisms require further exploration. In this study, we propose and fabricate an NH 3 sensor based on a Ti 3 C 2 T x MXene-functionalized U-shaped Tapered No-core fiber (UTNCF). This structure enhances the light-matter interaction with the MXene material through a strong evanescent field effect. Concurrently, we employed density functional theory (DFT) to systematically simulate the interaction between NH 3 molecules and Ti 3 C 2 T x with varying ratios of functional groups, calculating the band structure and charge transfer. Furthermore, the BoltzTrap module was utilized to analyze the changes in Ti 3 C 2 T x ’s optical refractive index upon NH 3 adsorption, thereby revealing the intrinsic physical mechanism of the sensor. Experimental results demonstrate that the developed sensor exhibits good performance over an NH 3 concentration range of 0–320 ppm. The sensor’s transmission spectrum shows a significant redshift with increasing NH 3 concentration, achieving a high sensitivity of 1.8 pm/ppm with good linearity. Theoretical calculations confirm that the primary sensing mechanism is the charge transfer from NH 3 molecules to the Ti 3 C 2 T x surface. This process alters the material’s carrier concentration, leading to a measurable change in its complex refractive index, which is in high agreement with our experimental observations. This work successfully combines theoretical calculations with experimental validation to not only develop a high-sensitivity fiber-optic NH 3 sensor but also to elucidate its sensing mechanism from a first-principle’s perspective. It provides an effective strategy for designing novel, high-performance Ti 3 C 2 T x -based optical gas sensors with significant application prospects in industrial safety and environmental monitoring.