Localized surface plasmon resonance aptasensor for the highly sensitive direct detection of cortisol in human saliva

•LSPR aptasensor has been developed for label-free detection of salivary cortisol with high sensitivity and selectivity.•Using the LSPR aptasensor, a wide range of cortisol concentrations (0.1–1000 nM) per a single droplet (5 μL) was detectable.•Our method was able to detect salivary cortisol, and the sensing performance was comparable to that of ELISA. Cortisol, which is a stress biomarker that causes various mental disorders, is found in sweat, saliva, blood, and urine. Because mental disorders resulting from stress are a silent contributor to various diseases, the detection of cortisol level is an important step in their prevention. Here, we developed a highly sensitive, localized surface plasmon resonance (LSPR) aptasensor for the direct detection of cortisol in saliva. The LSPR aptasensor was constructed using gold nanoparticles of different sizes. Subsequently, the surface of the LSPR substrate was immobilized using an aptamer for capturing cortisol. The detection capability of the LSPR aptasensor was compared with that of the antibody- immobilized sensor. The LSPR aptasensor displayed excellent detection capability for a wide range of cortisol concentrations extending from 0.1–1000 nM with a detection limit of 0.1 nM. In addition, the LSPR aptasensor was able to selectively detect cortisol among other substances with similar chemical structures (e.g., cortisone, corticosterone, progesterone, and triamcinolone). These results indicate that the LSPR aptasensor may be used for the highly sensitive and selective detection of cortisol in salivary samples.