Highly sensitive and non-invasive electrochemical immunosensor for salivary cortisol detection

•NiO thin film-based label-free electrochemical immunosensor has been devised using rf magnetron sputtering.•A low detection limit of 0.32 pg/mL in a broad range of linearity from 1 pg/mL to 10 μg/mL has been achieved.•The fabricated immunoelectrode possesses high selectivity against other common interferents.•The cortisol biosensor exhibits a stability of 9 weeks.•Cortisol in actual saliva samples have been successfully assessed and validated using standard ELISA. A non-invasive electrochemical immunosensor for detection of salivary cortisol has been proposed using RF sputtered NiO thin film as sensing platform. Cortisol, a steroid hormone, plays a vital part in administrating various physiological activities and also functions to be a stress biomarker. Thus, extremely sensitive and selective non-invasive mechanism for the detection of salivary cortisol has been focused in the present work. Covalently immobilized cortisol specific antibody on the NiO matrix has been used as the sensing platform. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) studies have been implemented to calibrate the electrode using standard cortisol solutions. The label-free immunoelectrode has been successfully devised and used to achieve detection limit as low as 0.32 pg/mL with high sensitivity in a broad range of linearity from 1 pg/mL to 10 μg/mL. It has been further assessed to detect cortisol in actual saliva samples and the results exhibit a great scope to foster the development of portable, integrated and efficient miniaturized non-invasive sensing devices for cortisol determination.