Session: Government Agency Student Posters

Paper Number: 173265

Scalable Binder-Free Fabrication of Gold-Zinc Oxide Ph Sensors via Plasma-Assisted Printing for Wearable Applications 

Developing robust and highly sensitive pH sensors is essential for diverse applications ranging from wearable healthcare monitoring to environmental sensing. Traditional pH sensors, particularly those based on metal oxides, frequently encounter limitations such as poor biocompatibility, limited durability, complex fabrication processes, and high-temperature sintering requirements incompatible with flexible substrates. To address these challenges, this study introduces a novel plasma-assisted direct printing method for fabricating zinc oxide–gold (ZnO–Au) hybrid nanostructures onto flexible substrates. This innovative, solvent-free, and binder-free technique significantly simplifies the sensor manufacturing process, enabling low-temperature deposition suitable for temperature-sensitive flexible substrates.

In this study, the ZnO sensing layer was fabricated using a plasma-assisted inkjet printing technique with an atmospheric plasma printer. The ZnO nanoparticle formulation was prepared by diluting an aqueous suspension of ZnO nanoparticles in a 1:20 ratio with deionized (DI) water. The ZnO nanoparticle structures were simultaneously deposited and plasma-treated directly from the precursor onto custom-fabricated flexible electrodes, ensuring uniform coating and enhanced surface interaction. The plasma printing was carried out using a 150:300 SCCM  of wet gas to dry gas and a printing voltage of 18 kV (peak-to-peak) at a frequency of 30 kHz. To induce localized surface plasmon resonance (LSPR), enhancing the sensor’s electrochemical response and improving its stability, a subsequent gold nanoparticle decoration was introduced above the ZnO layer. The gold chloride precursor was prepared by mixing aqueous HAuCl₄ with DI water in a 1:2 ratio, and gold nanoparticles were decorated via an in-situ plasma reduction of this gold chloride solution directly onto the previously printed ZnO layers.

Comprehensive structural and chemical characterization using scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) confirmed the successful formation of ZnO–Au hybrid nanostructures, highlighting enhanced crystallinity and improved material properties due to Au nanoparticle incorporation. Electrochemical evaluations through open-circuit potential (OCP) measurements demonstrated marked improvements in pH sensitivity, with ZnO–Au hybrid nanostructures achieving approximately 30% higher sensitivity (up to 39.1 mV/pH) compared to pure ZnO sensors (approximately 28.4 to 33.6 mV/pH). Cyclic voltammetry (CV) studies further revealed enhanced electron transfer kinetics and a significantly increased electrochemically active surface area (EASA), confirming the beneficial role of gold nanoparticles. Additionally, the hybrid sensors exhibited exceptionally low potential drift rates (<11 mV/h) compared to pristine ZnO, indicating outstanding stability and reliability for prolonged monitoring periods.

Selectivity testing against common physiological ions, including Na⁺, K⁺, Cl⁻, Mg²⁺, and Ca²⁺, showed minimal interference, demonstrating the sensor's high specificity and suitability for complex biological environments. Furthermore, rigorous mechanical durability assessments demonstrated stable sensor performance even after extensive mechanical stress, including 10,000 bending and twisting cycles performed using a fully automated, custom-built in-house setup to ensure consistency and repeatability. These attributes confirm the practical applicability and robustness of the ZnO–Au sensors for wearable biosensing applications.

The plasma-assisted direct printing method provides a scalable and efficient pathway for producing advanced ZnO–Au hybrid pH sensors. The enhanced sensitivity, selectivity, stability, and mechanical durability achieved by these ZnO–Au hybrid sensors establish them as highly promising solutions for real-time, continuous physiological monitoring in wearable healthcare systems and environmental sensing applications.

Presenting Author: Santhosh Adhinarayanan Norfolk State University

Presenting Author Biography: Santhosh Adhinarayanan received his B.Tech degree in Electronics and Instrumentation Engineering with a Minor in Entrepreneurship from Pondicherry University, India, in 2022, and is currently pursuing his M.S. degree in Electronics Engineering at Norfolk State University, USA. He is currently a Graduate Research Assistant in the Department of Engineering at Norfolk State University, Norfolk, Virginia, USA. His research interests include plasma-aided inkjet printing, biosensors, nanoelectronics, and point-of-care diagnostic devices.

Authors:

Santhosh Adhinarayanan Norfolk State University
Harikrishnan Muraleedharan Jalajamony Norfolk State University
Soumadeep De Norfolk State University
Markee Watson Norfolk State University
Renny Fernandez Norfolk State university