Demonstration of sweat-based circadian diagnostic capability of SLOCK using electrochemical detection modalities.

SLOCK is a sweat-based circadian diagnostic platform used for mapping the user's chronobiology via cortisol and DHEA. In this work, we have demonstrated the detection capabilities of this sweat-based sensing platform using two electrochemical sensing modalities: Electrochemical Impedance Spectroscopy (EIS) and chronoamperometry. Wicking simulations for vertical versus horizontal flow patterns under potential bias were evaluated using COMSOL Multiphysics®. This work also highlights the biorecognition element characterization using Surface Plasmon Resonance (SPR) and FTIR. Sensor platform was evaluated for biomarker concentrations using doses spanning physiological ranges of 8-141 ng ml -1 and 2-131 ng ml -1 for cortisol and DHEA, respectively. Detailed analysis of impedance data is supported with electrochemical fitting of circuit components related to the biosensing process. Finally, human subject-based studies have been performed to understand the effect of sweating rate with respect to gland density on biosensing. Also, on-body mechanical resiliency studies have been performed to highlight the flexibility of this serpentine electrode-based sensing platform. The platform responds sensitively to the amount of circadian relevant biomarkers in the system with a limit of detection of 0.1 ng ml -1 for both cortisol and DHEA. Thus, the SLOCK platform offers to be an attractive vessel for facilitating the electrochemical detection of circadian relevant biomarkers and for self-monitoring of user's chronobiology.