Session: 14-10-02: Micro/Nanofluidics 2025 II

Paper Number: 166182

Zinc Oxide Nanowalls Based Flexible and Non-Invasive Electrochemical Cortisol Sensor 

Chronic stress is a significant concern in modern society, adversely affecting mental health and overall well-being. Cortisol, a key biomarker of stress, plays a crucial role in regulating metabolic processes, immune responses, and cardiovascular health. Abnormal cortisol levels are associated with severe health conditions such as Cushing's syndrome, hypertension, anxiety disorders, cardiovascular diseases, and metabolic syndromes. Consequently, the accurate monitoring of cortisol concentrations is essential, particularly for individuals exposed to high-stress environments, including patients with endocrine disorders, athletes, military personnel, and individuals managing chronic stress-related conditions. Sweat, a biofluid that is readily accessible and analyzable, provides a promising alternative to blood sampling for noninvasive cortisol detection. Unlike blood and saliva, sweat collection is painless, convenient, and ideal for continuous monitoring, making it highly suitable for wearable biosensors. The dynamic and real-time nature of sweat-based cortisol assessment enables a comprehensive understanding of physiological stress responses without the discomfort or inconvenience of traditional invasive sampling techniques. Recent advancements in nanomaterial-based biosensing technologies have significantly improved sensor sensitivity, specificity, and real-time monitoring capabilities. Flexible wearable biosensors based on zinc oxide (ZnO) nanostructures are a powerful tool for detecting cortisol in sweat and it is a noninvasive approach to monitor stress levels. Among these, ZnO nanowalls (ZnO-NWs) stand out due to their large surface area, highly interconnected porous structure, and exceptional ability to capture biomolecules, making them particularly well-suited for biosensing applications. ZnO-NWs are characterized by vertically aligned, thin, and interconnected crystalline plates that form a three-dimensional (3D) open-framework architecture. Their unique morphology significantly enhances sensor performance by facilitating rapid charge transport, minimizing electron recombination losses, and improving analyte diffusion to the active surface. The high-aspect-ratio structure of ZnO-NWs provides an extensive electroactive interface, which is essential for immobilizing biomolecules such as antibodies or enzymes while maintaining their bioactivity. A sonochemical synthesis approach was employed to fabricate a ZnO-NWs layer on a flexible polyethylene terephthalate (PET) substrate coated with gold (Au), where ultrasonic cavitation generates localized high temperatures and pressures, driving the nucleation and anisotropic growth of ZnO. Additionally, the inherent high isoelectric point of ZnO (9.5) facilitates strong electrostatic interactions with biomolecules, enhancing antibody binding efficiency without requiring additional surface functionalization. This property eliminates the need for complex chemical modifications and ensures a more stable and reproducible sensing interface. The vertically aligned nanowall configuration also improves electron transport pathways, reducing charge transfer resistance and enhancing the sensor’s overall electrochemical performance. Furthermore, the porous nature of ZnO-NWs allows for efficient diffusion of analytes, ensuring rapid and sensitive detection. The sensor was meticulously engineered by immobilizing anti-cortisol antibodies (Anti-C_AB) onto the ZnO-Ns matrix, culminating in the formation of a highly responsive nanostructured interface serving as the working electrode. The constructed PET/Au/ZnO-NWs/Anti-C_AB biosensor exhibited a remarkable sensitivity of 247 µA/decade/cm² μA/decade/cm², with an impressively low detection threshold of 0.1 pM. Furthermore, the coefficient of determination (94.03%) underscored the sensor’s exceptional linearity across a broad dynamic range.

Presenting Author: Tiham Fayaz The University of Texas Rio Grande Valley

Presenting Author Biography: Tiham Fayaz holds a Bachelor of Science degree in Electrical and Electronic Engineering from Chittagong University of Engineering and Technology, where his undergraduate research focused on renewable energy. Currently pursuing a Master’s degree in Electrical and Computer Engineering at The University of Texas Rio Grande Valley, his research interests encompass energy harvesting, semiconductor materials, biosensors, micro- and nanofabrication, and VLSI design.

Authors:

G M Mehedi Hossain The University of Texas Rio Grande Valley
Tiham Fayaz The University of Texas Rio Grande Valley
Ahmed Hasnain Jalal The University of Texas Rio Grande Valley
Hasina Huq The University of Texas Rio Grande Valley
Nazmul Islam The University of Texas Rio Grande Valley
Nezih Pala Florida International University
Karen Lozano Rice University
Fahmida Alam The University of Texas Rio Grande Valley