<p>A novel nanocomposite, CoS₂-CoO/poly-O-aminobenzenethiol (CoS₂-CoO/POABT), has been synthesized in the form of open-spherical nanostructures, where the CoS₂-CoO dopant is seamlessly embedded within the POABT matrix. These unique spheres feature walls approximately 25 nm thick, surrounding an open cavity with a diameter of around 40 nm. Harnessing its exceptional structural and electrochemical properties, this CoS₂-CoO/POABT nanocomposite is employed as a potentiometric sensor for detecting Cd²⁺ ions in aqueous solutions. The sensor operates effectively in both two- and three-electrode systems, utilizing simple and cyclic voltammetry techniques. It exhibits an impressive potentiometric slope of 27.5 mV per decade across a Cd²⁺ concentration range of 10^-5 to 10^-1 M, with a remarkable detection limit of 4 × 10^-6M. Additionally, cyclic voltammetry analysis reveals a sensitivity of 3 × 10^-6 A/M, highlighting its exceptional precision and responsiveness. Notably, this sensor demonstrates outstanding selectivity for Cd²⁺ ions, maintaining its accuracy even in the presence of potential interfering species such as Zn²⁺, Ca²⁺, Ni²⁺, Al³⁺, K⁺, and Mg²⁺. To further validate its real-world applicability, the sensor is tested using natural samples, confirming its reliability for environmental monitoring. With its high sensitivity, selectivity, and practical utility, the CoS₂-CoO/POABT nanocomposite sensor emerges as a powerful tool for trace-level Cd²⁺ detection in environmental and analytical applications.</p>