In this paper, an acetone sensor based on a single-mode fiber (SMF) coated with cobalt oxide (Co \(_{3}\) O \(_{4}\) ) nanoparticles is characterized. Different methods were explored for coating Co \(_3\) O \(_{4}\) nanoparticles on SMF, and a chemical vapor etching (CVE) method was optimized to yield a functionalized SMF. The Co \(_3\) O \(_{4}\) nanoparticles were synthesized via coprecipitation using cobalt acetate and NaOH. SEM analysis showed that CVE pretreatment created a distinct surface morphology, enabling a more uniform and homogeneous nanoparticle coating compared to the dip coating method. Extensive material characterization methods such as Fourier transform infrared (FTIR), Ultraviolet-Visible (UV-Vis) spectroscopy, dynamic Light Scattering (DLS) analysis, and scanning electron microscope (SEM), are utilized to analyze and evaluate structural stability and homogeneous distribution with optical properties of the nanoparticles and their applicability in breath analysis. A customized sensor characterization setup has been designed for acetone sensing. An optical coupler injects light into the fiber, while another directs the transmitted signal to a photodiode, which converts it into an electrical current varying with acetone concentration. This signal is processed by a microcontroller (Arduino/ESP-32). The output current increases from 0.48 \(\mu\) A at 0.5 ppm to 2.6 \(\mu\) A at 12 ppm, yielding a sensitivity of 0.18 \(\mu\) A/ppm with 3% non-linearity. The sensor offers a low-cost, high-performance solution for acetone detection for early diagnosis and health monitoring, supporting sustainable healthcare and innovation.
