ANALYTICAL DETERMINATION OF CORTISOL USING A FLUORESCENT APTAMER ASSAY

Cortisol is a steroid hormone that stimulates gluconeogenesis. A high cortisol concentration in saliva can be an indication of stress and a low concentration can indicate metabolic problems. By monitoring the level of cortisol one can determine and perhaps mitigate their stress levels. Aptamers or chemical antibodies are DNA or RNA sequences (10-100 nucleic acids) that are made synthetically and selected to bind to cells, proteins and small molecules. These molecules can have similar or better affinity and specificity compared to antibodies and are widely used in diagnostics. Since aptamers are composed of nucleotides it is possible to use specific fluorescent tags and intercalating dyes. Here we developed a sensor for detecting cortisol using an aptamer specific for cortisol and a forced intercalating probe (FIT) composed of thiazole orange (TO). The aptamer was saturated with TO and the decrease in fluorescent intensity was measured as a result of the aptamer binding to cortisol. The samples were measured in Tris buffer and in an artificial saliva matrix. The present results demonstrate an inexpensive, yet sensitive technique to measure cortisol in saliva.