Portable biosensor for monitoring cortisol in low-volume perspired human sweat

A non-faradaic label-free cortisol biosensor was demonstrated using MoS₂ nanosheets integrated into a nanoporous flexible electrode system. Low volume (1-5 μL) sensing was achieved through use of a novel sensor stack design comprised of vertically aligned metal electrodes confining semi-conductive MoS₂ nanosheets. The MoS₂ nanosheets were surface functionalized with cortisol antibodies towards developing an affinity biosensor specific to the physiological relevant range of cortisol (8.16 to 141.7 ng/mL) in perspired human sweat. Sensing was achieved by measuring impedance changes associated with cortisol binding along the MoS₂ nanosheet interface using electrochemical impedance spectroscopy. The sensor demonstrated a dynamic range from 1-500 ng/mL with a limit of detection of 1 ng/mL. A specificity study was conducted using a metabolite expressed in human sweat, Ethyl Glucuronide. Continuous dosing studies were performed during which the sensor was able to discriminate between four cortisol concentration ranges (0.5, 5, 50, 500 ng/mL) for a 3+ hour duration. Translatability of the sensor was shown with a portable form factor device, demonstrating a comparable dynamic range and limit of detection for the sensor. The device demonstrated a R² correlation value of 0.998 when comparing measurements to the reported impedance values of the benchtop instrumentation.