Carbon quantum dot-aptamer/MoS₂ nanosheet fluorescent sensor for ultrasensitive, noninvasive cortisol detection

This work presents the development of a highly sensitive, selective, and efficient aptamer-based fluorescent sensor for detecting cortisol in human urine. Carbon quantum dots-nucleic acid aptamer (CQDs-Apt) synthesized with excellent photoluminescent properties and stability, were selected as the fluorescent probe. In the presence of MoS₂-NSs, CQDs-Apt adsorbed onto the surface of MoS₂-NSs via electrostatic and π-π interactions, leading to strong and rapid fluorescence quenching due to static quenching mechanism between them. The CQDs-Apt/MoS₂-NSs complex can be employed as a "turn-on" fluorescent sensor for cortisol. Upon the addition of cortisol to the CQDs-Apt/MoS₂-NSs sensor, the aptamer specifically binds to cortisol, thereby weakening the interaction between CQDs-Apt and MoS₂-NSs. This results in the desorption of CDs-Apt from the surface of MoS₂-NSs and the recovery of the fluorescence signal. Under optimized conditions, the CQDs-Apt/MoS₂-NSs sensor exhibits a linear response to cortisol concentration (1-500 ng/mL) with a detection limit of 0.3 ng/mL. Furthermore, the sensor demonstrated excellent stability, high accuracy (92.0% to 97.7%), and superior precision (RSD ≤ 3.5%). This sensor has achieved a sensitive, rapid and efficient response to cortisol, and been successfully utilized for the detection of cortisol in human urine, demonstrating its potential for clinical cortisol detection.