Cortisol
Volume Requirements
25 ul saliva/replicate
(150ul required for testing to account for pipetting needs and sample quality)
Assay Range
0.012 - 3.000 ug/dL
Assay Sensitivity
0.007 ug/dL
Compatible Collection Methods
Passive Drool
Swab
Special Considerations
Hormonal based contraceptives, steroid creams, and other medications can impact cortisol results.
Cortisol demonstrates a diurnal rhythm. Collect samples from each participant several times (3-5x) across a day for at least two days if possible, or collect samples from participants at the same time a day for most accurate comparisons between participant samples.
Methodology
Saliva is tested at IISBR using a commercially-available enzyme-linked immunosorbent assay kit (ELISA) from Salimetrics following manufacturer’s protocol without modification. This test employs a 96-well microtitre plate coated with a monoclonal antibody (Ab) to cortisol. Cortisol in standards, controls and unknown samples compete with cortisol linked horseradish peroxidase (HRP) for available antibody binding sites. Bound cortisol peroxidase is measured by the reaction of the peroxidase enzyme on the substrate tetramethylbenzidine (TMB) producing a blue color. The reaction is stopped and the resultant yellow color is read at 450nm on a spectrophotometer (PowerWave HT, BioTek Instruments). The amount of cortisol peroxidase detected, as measured by the intensity of color, is inversely proportional to the amount of cortisol present.
Briefly, 25 µL of standard, controls, and unknown saliva are pipetted onto 96-well microtitre plates and incubated for 1 hour shaking with cortisol conjugated to HRP at room temperature. Plates are washed 4 times followed by addition of a TMB substrate and incubation at room temperature in the dark for 30 minutes. Following incubation, the reaction is stopped with 2M Sulfuric Acid (NH2SO4)and optical density (OD) read at 450nm with a 490nm correction filter. Concentrations of controls and samples are calculated from a standard curve generated using a 4-parameter non-linear regression curve fit (Gen5, BioTek).