In-direct localized surface plasmon resonance (LSPR)-based nanosensors for highly sensitive and rapid detection of cortisol

Over-secretion of cortisol from the adrenal cortex is closely related to acute and chronic stress; thus, rapid and sensitive detection of cortisol in serum is of critical importance for preventing the progression of stress-related diseases. The binding of a biological molecule to the surface of metallic nanoparticles changes the local refractive index and in turn induces a shift in the localized surface plasmon resonance (LSPR) wavelength. Utilizing this phenomenon, we designed a novel disposable LSPR-based cuvette-type sensor for detecting cortisol in serum. The developed cuvette-type nanosensor consists primarily of an assembly of plastic unit sensors coated with gold nanoparticles on a single layer wherein cortisol-conjugated bovine serum albumin (BSA) is immobilized. In this system, a redshift in LSPR wavelength is induced by the binding of cortisol antibody onto cortisol-conjugated BSA immobilized on a gold nanoparticle surface in the nanosensor. In a competitive assay, the nanosensor could rapidly detect cortisol in both a PBS solution and serum (within 20 min) at concentrations ranging from 1 to 10,000 ng/mL (2.759-3 × 103 nmol/L), which is comparable to conventional enzyme-linked immunosorbent assay (ELISA) which typically requires longer than 4 h and complex sample preparation. Thus, we demonstrated that the LSPR-based nanosensor system developed in this study can provide a useful toolkit for a rapid, highly sensitive and reliable detection of cortisol hormone in a commercially available manner.