The effect of different hydrocortisone concentrations was tested with the FID assay on the TO-cortisol aptamer complex (1/0.05 µM) to determine the concentration of cortisol in saliva (3a). The percentage decrease of fluorescent intensity in figure indicates a linear trend showing that an increased concentration of hydrocortisone leads to a lower fluorescent intensity of TO. The lowest observed concentration of hydrocortisone (0.05 µM) is detectable with a 14.21% decrease in TO fluorescence, while the a concentration of 0.5 µM results in a decrease of fluorescence of 21.57%.