Single-walled carbon nanotubes (SWCNTs) have been widely exploited in recent years as highly adsorbent nanocoatings on optoelectronic sensors for chemical detection in air and water. 1–3 Excellent sensing performance has been obtained so far, such as detection limits of less than one part per million (ppm), high repeatability, and response times of few minutes. Nevertheless, the adhesion of carbon nanotubes to the fiber end-face still represents a challenge that must be addressed for practical applications and before the sensors can be commercialized. We propose the use of sensitive coatings composed of a nanocomposite material of SWCNTs embedded in cadmium arachidate (CdA) matrixes to improve the robustness and sensitivity of the optoelectronic chemical sensors. The experimental results demonstrate that such a composite integrated with optical fiber technology offers great potential for room-temperature detection of trace chemicals in water and could lead to significant improvements of optical fiber sensors based on standard SWCNT layers. To the best of our knowledge, no experimental data has been reported before on the capability of such nanoscale coatings to detect chemicals in liquid environments. The sensor configuration is based on a low-finesse Fabry–Pérot interferometer created by the deposition of thin sensitive nanocoatings on the terminal face of standard single-mode fibers (see Figure 1). The presence of the analyte molecule changes the nanocoating’s refractive index and thickness. When light is transmitted through the fiber to this sensing layer, these changes modulate the intensity of light reflected back into …