Developing highly sensitive and selective sensors is important for the detection of steroid hormones. Electrochemical sensors are of great interest in this regard. Also utilization of bio-derived substances as an electrode material is environment friendly. In this study, we used green-synthesized cobalt oxide nanoparticles (CoO NPs) along with nafion (Naf) on a glassy carbon electrode to detect hydrocortisone (HC) by voltammetry. Electron microscopy, X-ray diffraction, Raman spectroscopy, ultraviolet–visible spectroscopy, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy were used to characterize the CoO NPs prepared using Nigella sativa seeds extract. Cyclic voltammetry and differential pulse voltammetry was utilized for the detection of HC. Only one reduction peak at −0.5 V was observed in the presence of HC in 0.1 M sodium hydroxide, indicating an irreversible electrode process. The Naf-CoO NPs enhanced the active surface area of the glassy carbon electrode (GCE) that resulted in a good response for detecting HC with two linear ranges: 0.001–1 μM and 1–9 μM. In comparison to other published electrochemical sensors, the current sensor displayed a low limit of detection of 0.49 nM, as well as remarkable stability and reproducibility. The sensor exhibited credibility for the sensing of HC in pharmaceutical injections and blood serum samples with recovery percentages ranging from 97.7% to 102.5%. The electrochemical sensor has proved to be valuable for HC detection.
