Specific Detection of Cortisol in Biological Fluids: A Tailored Electrochemical Aptasensing Approach

Cortisol is a key endogenous hormone involved in physiological and pathological processes, its levels fluctuating in biological fluids due to numerous factors, including inflammatory disorders. Therefore, the accurate and selective detection of cortisol is essential for both diagnosing these conditions and evaluating treatment efficiency. Electrochemical methods offer significant advantages for biomarker analysis in biological samples due to their low cost, high sensitivity and specificity, potential for miniaturization, and capability for in situ analysis. The goal of this study was to design a customized platform for the specific electrochemical detection of cortisol in biological samples, with potential applications in portable biomedical devices. Flexible, customized carbon electrodes were fabricated, and the surface of the working electrodes was modified using Au and Pt, to enhance sensitivity, and an aptamer to increase specificity for cortisol detection. All the modification steps were validated using cyclic voltammetry, electrochemical impedance spectroscopy, and X-ray photoelectron spectroscopy. Cortisol detection was performed via cyclic voltammetry, and the platforms were assessed for their analytical performance, including the limit of detection, limit of quantification, and sensitivity. The aptasensor was able to determine the analyte on a linear domain between 0.5 and 100 nM, with a limit of detection of 0.1 nM. Additionally, the aptasensors were applied for the analysis of saliva and sweat samples collected from patients and healthy subjects as control. This aptasensor enables the specific detection of cortisol and has the potential to be further developed for point-of-care medical applications.