Interfacial Tuning for Detection of Cortisol in Sweat Using ZnO Thin Films on Flexible Substrates

We have demonstrated the detection of stress hormone cortisol from sweat using a flexible biosensing platform. Sweat-based detection faces many challenges such as stability of electrodes, sensitivity, and specificity. The surface states of zinc oxide (ZnO) can be leveraged for immobilizing various linker molecules for ultraspecific detection of biomolecules. In this study, we have used thiol-based linker molecule for binding to zinc terminations. We tested DSP from 5 to 100 mmol concentration in order to understand the effect of varying molarity on the electron transport properties of ZnO thin films. We performed electrochemical impedance spectroscopy measurements and Mott-Schottky analysis after incubation of the dispensed DSP linker on ZnO thin films. The optimized concentration of DSP was further incorporated in the immunoassay for detection of cortisol from 1 to 200 ng/mL spiked in sweat.