Initially, an experimental proof of concept was conducted with the cortisol binding aptamer together with a reporter (TO) to determine the concentration of cortisol in saliva. As a background it was essential that the cortisol aptamer, free TO, hydrocortisone and HS Tris buffer did not contribute significantly to the fluorescence nor that the presence of hydrocortisone would make the TO increase its fluorescent signal. The fluorescence of free TO in solution is an order of magnitude smaller than when TO is intercalated into DNA . Hydrocortisone can change the conformation of the cortisol aptamer which forces TO to leave the aptamer resulting in a decrease in fluorescence .