Surface-specific washing-free immunosensor for time-resolved cortisol monitoring

Cortisol is a steroid hormone that regulates a wide range of vital processes. Its level changes with diurnal rhythm and reacts to stress. Measurement of cortisol levels is still a complex multi-step process. A reversible washing-free registration method is required. Here we describe metal-enhanced fluorescence assay based on a displacement of a dye labeled BSA-cortisol conjugate from the immune complex immobilized on the golden islands by free cortisol. This competitive approach allows time-resolved monitoring of the fluorescent signal, surface-enhanced by the gold film, and provides the possibility of continuous real-time cortisol monitoring based on the implantable surface-enhanced immunosensor, which was not demonstrated so far even in vitro.