Biosensors are emerging as essential tools in medical diagnostics due to their ability to rapidly and accurately detect biomarkers. A biosensor typically consists of a bioreceptor that recognises a target molecule, a transducer that converts this interaction into a measurable signal, and a display system for interpretation (1). Cortisol is a critical biomarker involved in stress regulation, metabolism, immune function, and cardiovascular health (2). It follows a circadian rhythm, peaking in the early morning and reaching its lowest levels around midnight (3). Dysregulation of cortisol levels is implicated in conditions such as Cushing’s syndrome, Addison’s disease, and metabolic syndrome (4-6).
Despite the clinical significance of cortisol, existing methods for its quantification are significantly limited, requiring laboratory infrastructure, long turnaround times, and a lack of portability (7-8). Currently, no commercially available point-of-care or wearable biosensor exists for cortisol detection. Electrochemical biosensors represent a promising alternative due to their portability, affordability, and potential for miniaturisation (9). Sensitivity can be further enhanced by incorporating nanomaterials (10-11). Antibody-based sensors also offer high specificity for cortisol recognition (12).
This project proposes the development of a novel electrochemical cortisol biosensor employing antibody-functionalised gold nanoparticles. Propargyl-PEG₄-thiol will be used to functionalise the gold nanoparticle surface, while azido-PEG₁₂-NHS ester will modify the anti-cortisol antibody. The azide-antibody conjugate will react with the propargyl-modified nanoparticles, forming a stable triazole linkage. Conjugation will be verified using ultraviolet-visible spectrophotometry, and commercially available hydrocortisone will serve as a positive control. The functionalised nanoparticle will be incorporated into an electrochemical transducer platform designed for use with human saliva samples.
This biosensor is intended for integration into wearable and point-of-care systems, offering a sensitive, specific, and non-invasive method for real-time cortisol monitoring. Such technology could enable improved diagnosis and management of endocrine and stress-related disorders in both clinical and remote settings.