Green synthesis technology was applied to manufacture a nanoelectrode that senses cobalt ions for the first time using the organic precipitant (4-(3-(2-(3-hydroxyphenyl)-4,7-dioxo-1,3-oxazepin-3(2H, 4H, 7H).)-yl) thioureido) benzenesulfonamide). The electrode manufacturing precipitate was prepared by reacting to the organic precipitant with cobalt oxide nanoparticles prepared from the Conocarpus plant extract using a simple green method. The prepared particles were characterized using X-ray diffraction, scanning electron microscopy, and infrared techniques. They were shaped like cauliflower leaves and had an average particle size of 17.86–49.13 nm. The manufactured electrode shows a linear range of concentrations 1 × 10–1–1 × 10–11 with a molar slope of 18.3 mv/decade. The electrode was operated at temperatures 15–50 °C and an acid function of 1–6. The response time was less than 37 s, the age of the electrode was 61 days, the recall ranges between 100.5–100.03, and the detection limit is 12.33 × 10–11 molarity. This electrode was used to sense cobalt ions in contaminated water samples.