TISS nanobiosensor for salivary cortisol measurement by aptamer Ag nanocluster SAIE supraparticle structure

The aptamer based signal-on nanobiosensor for measuring salivary cortisol in the nanomolar level is presented for the first time in this study. Cortisol, as a stress biomarker, plays a critical role in physiological mechanisms. Measurement without contamination by needle stress is the main advantage of cortisol measurement in saliva. Salivary cortisol quantity is much lower than serum cortisol, so overcoming the measurement challenge requires new ultrasensitive detection methods. In the presented Target-Induced Structural Switching mode Aptamer (TISS) nanobiosensor, the ssDNA aptamer plays the role of transducer moiety and biorecognition module simultaneously. The aptamer structure has sequence against cortisol in the middle and two cytosine reach compartments in 3^' and 5^' ends which are designed for Ag-NC supramolecule configuration. The molecule-like properties of the Ag nanocluster create a strong AIE fluorescence signal. Binding aptamer to cortisol causes proximity of Ag-NCs supraparticles and leads to aggregation base fluorescence enhancement. 1 nmol/l as LOD and 1 nmol/L to 900 nmol/L for linearity achieved by presented salivary cortisol nanobiosensor. This assay was performed in one single tube without further stages as a mix and measure method.