Salivary cortisol detection by novel hollow AgAu nanoislands plasmonic-based sensor

The intricate process of hormone secretion reveals critical health indicators, including metabolism, stress, and emotional well-being. Cortisol monitoring, in particular, is a valuable diagnostic tool for physical and psychological health. This study introduces a salivary cortisol biosensor by applying a novel type of hollow AgAu nanoislands (HAgAu NIs) materials with enhanced plasmonic effect. The synthesized hollow metallic nanoislands, characterized by their distinctive empty inner cavities, exhibit significantly enhanced localized surface plasmon resonance (LSPR) effect that exceeds conventional solid nanoislands. This enhancement arises from the additional interactions of the plasmon acting on the empty cavity and solid shell, resulting in a greater electric field under light illumination. The enhanced plasmonic effect was analysed through both computational and experimental methods, Finite-Difference Time-Domain (FDTD) simulation reveals an increased electric field in hollow nanoparticles, and experimental results showed improved sensitivity in LSPR-based sensing. The resulting stronger plasmonic effect enhances the biosensing capabilities, showing nearly double the sensitivity compared to conventional nanoislands. Notably, antibodies functionalized HAgAu NIs demonstrated excellent sensitivity for detecting cortisol with a 12.68 pg/ml limit of detection. The salivary cortisol detection, ranging from 0.5 ng/ml to 25 ng/ml, showed linearity with R 2 = 0.978, highlighting the practicality and reliability of the developed sensor for clinical applications. In comparison to traditional immunosensors, the demonstrated LSPR-based biosensor offers time-saving and cost-effective functionalities through real-time monitoring and exceptional sensitivity. • Hollow nanostructure facilitates plasmonic field enhancement. • Rapid, non-invasive cortisol sensing in human saliva. • Facile fabrication of hollow nanoislands stable in air and aqueous environments • Electric field enhancement in hollow nanostructure explained via FDTD simulation. • The proposed plasmonic sensor was label-free, highly sensitive and cost-effective.