ZnO Nanorod Integrated Flexible Carbon Fibers for Sweat Cortisol Detection

Abstract

Sensors fabricated on fabrics provide an elevated ease of use for wearable sensors. Such sensors will play a critical role in detecting the elevations in the concentrations of biochemical markers in human sweat. The ability of making such measurements is becoming an important tool for non-invasive and real-time health monitoring. We present a yarn-based flexible and superwettable electrochemical immunosensing strategy for highly selective and sensitive detection of cortisol in sweat. ZnO nanorods (ZnONRs)-coated flexible carbon yarns were prepared by using a hydrothermal method for immobilizing specific anti-cortisol antibodies and used as an immunosensing platform for detecting sweat cortisol levels. The morphology, elemental composition, crystallinity, and specific surface area were analyzed by using analytical techniques such as transmission electron microscopy (TEM), field emission scanning electron microscopy coupled energy-dispersive X-ray analysis (FE-SEM/EDS), X-ray diffraction (XRD), fourier-transform infrared spectroscopy (FT-IR), Raman spectroscopy, and Brunauer–Emmett–Teller (BET) analysis. The ZnONRs integrated carbon yarns showed excellent mechanical stability and superwettable properties. The immunosensor exhibited a wide linear detection range from 1 fg/mL to 1 μg/mL. The detection limits of the immunosensor were calculated to be between 0.45 and 0.098 fg/mL by using CV and DPV techniques, respectively. Additionally, cell viability studies were performed to investigate the biocompatibility and cytotoxicity of this carbon yarn ZnO sensing platform. The immunosensor was applied to measure the cortisol concentration in human sweat samples, and the outcomes were validated by using a chemiluminescent immunoassay system.

Flexible Biosensors Based on Colorimetry, Fluorescence, and Electrochemistry for Point-of-Care Testing

“…In addition, carbon fibers possess favorable conductivity and have a promising future in the field of textile-based sensors. Madhu’s group proposed a flexible yarn-based electrochemical immunosensing method for the analysis of sweat cortisol ( Madhu et al, 2020 ). As shown in Figure 3C , ZnO nanorods (ZnONRs) were coated onto flexible carbon yarns using a hydrothermal treatment to facilitate the immobilization of specific anti-cortisol antibodies.…”

“…(B) Specially designed universal paper-based electrochemical sensor (Liu et al, 2019b). (C) Schematic diagram of a zinc oxide nanorod electrochemical sensing electrode integrated with flexible carbon fibers for sweat cortisol detection (Madhu et al, 2020). 0-600 μM concentration range, exhibiting comparable performance to conventional sensors based on carbon materials.…”

Differential responses of salivary cortisol, amylase, and chromogranin A to academic stress

“…So the application of using saliva to monitor stress real-time and on-site is still in its early stage of practice. More recently, the wearable biosensor that can measure cortisol in sweat is being developed [ 57 , 58 ]. This could be very important in stress research to measure cortisol real-time and it can be applied to be used like a smart watch to monitor stress in the future.…”

Expanding Horizons of Metal Oxide‐based Chemical and Electrochemical Sensors

“…The sensor employed anti‐cortisol antibodies immobilized onto ZnO/CCY blocked by BSA for enhanced specificity. The response current dropped upon increasing cortisol concentration due to formation of an insulating Ag−Ab complex that prevents mass and electron transfer between the electrolyte and the electrode [19]. ZnO nanoflakes formed via a single‐step sonochemical method were used to measure the levels of an oxidative stress marker, L‐lactate in sweat in concentrations as low as 1.26 nM with a current sensitivity of 11.76 μA/decade/cm 2 by functionalizing lactate oxidase on the nano‐interface.…”