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[Display omitted] • Need for economic growth led to the development of fiber optic-based sensors. • Coupling of metal oxides permits redox reactions supporting sensing property. • TiO 2 -ZnO composites (S1) and annealed 500 °C (S2) & 1200 °C (S3) in sensing study. • Enhanced sensitivity and selectivity in S3 sensor for ammonia at room temperature. • The rise and fall time of the S3 sensor were 18 sec and 15 sec respectively. Fiber optic sensors, promising for their compactness and remote sensing abilities, are explored in this study as a platform for detecting volatile organic compounds (VOCs) using nanocrystalline metal oxide composites like TiO 2 -doped ZnO. Hydrothermally synthesized (S1 sample)and annealed composites (500 °C (S2 sample) and 1200 °C (S3 sample) annealing) were investigated for their gas-sensing properties towards inorganic gas like ammonia and VOCs like acetone, and isopropyl alcohol. Remarkably, annealing at 1200 °C yielded S3 sample with higher response (7.5 %) towards ammonia at room temperature for 500 ppm concentration. This superior performance is attributed to increased surface area, narrowed bandgap, and faster response/recovery times (18/15 s) compared to other samples. The proposed sensing mechanism involves the adsorption and desorption of oxygen molecules on the sensor surface, altering refractive index and light scattering, ultimately modulating the transmitted light intensity. X-ray diffraction, SEM imaging, and UV–Vis absorption techniques confirmed the structure and morphology of the nanocomposites. [ABSTRACT FROM AUTHOR]

• Evanescent fiber optic sensing and DFT approach in graphite pencil powder introduced. • Black graphite pencil powder exhibited better sensitivity for ethanol at room temperature. • DFT analysis supported the experimental results with better adsorption energy and distance. This study investigated the ethanol-sensing properties of pencil graphite using a fiber optic gas sensor. The results were further confirmed using density functional theory (DFT). The sensor showed good sensitivity (18 counts/100 ppm) and response time (70 sec). The electronic analysis of pure and ethanol-adsorbed graphite powders was also conducted using their band structures, Density of States (DOS), and projected Density of States (PDOS). For ethanol-adsorbed graphite, it was shown that there were significant alterations in band structure and density of states, providing insights for gas sensing applications. [ABSTRACT FROM AUTHOR]