Microfluidic Electrochemical Sensor for Online Detection of Chemical Oxygen Demand Based on AuNPs/Au Electrodes
Water pollution caused by urbanization and industrial activities has significantly increased the demand for effective water quality monitoring. Chemical oxygen demand (COD) is a crucial indicator of organic pollution in water, traditionally measured using methods involving toxic chemicals and time-consuming processes. This study presents a novel microfluidic electrochemical sensor based on gold nanoparticle-modified electrodes (AuNPs/Au), designed to provide a fast, reliable, and eco-friendly way of online COD detection.
The sensor integrates an interdigital gold (Au) electrode with gold (Au) nanoparticles deposited through an electrodeposition method. This modification enhances the electrocatalytic performance and stability of the electrode. The device is further combined with a polydimethylsiloxane (PDMS) microfluidic system, enabling controlled flow and reaction conditions. The compact design, measuring just 30 × 10 × 5 mm, allows for easy integration into monitoring systems.
The interdigital Au electrode was activated and functionalized in the fabrication process with a dense layer of Au nanoparticles using cyclic voltammetry and chronoamperometry techniques. The PDMS microfluidic system was created through standard photolithography and molded to fit seamlessly with the electrode. Together, these components form a stable, high-performance sensor capable of accurately measuring COD.
The sensor was tested with glucose solutions as COD standards, demonstrating a broad detection range of 0–400 mg/L and a low detection limit of 0.12 mg/L, surpassing the Chinese national standard of 20 mg/L. Its electrochemical performance was validated using cyclic voltammetry, showing significant improvements in current response and redox capacity compared to unmodified electrodes. Real-time measurements were achieved in under three minutes without the need for any toxic reagents, making the process both efficient and environmentally friendly.
The sensor's effectiveness was further confirmed by testing water samples from five locations in a lake. The results closely matched those obtained from standard ISO6060 methods, with relative errors ranging from 3.7% to 8%. This highlights the sensor's reliability in real-world applications.
A comparison with existing COD sensors revealed that the AuNPs/Au sensor offers superior sensitivity, a wider detection range, and the ability to perform online measurements. It achieves a low detection limit of 0.12 mg/L and a broad linear range (0–400 mg/L). Its compact size and low production cost make it suitable for mass production and commercial applications. Moreover, its eco-friendly design aligns with the growing need for sustainable water monitoring technologies.
In conclusion, this study demonstrates the potential of microfluidic electrochemical sensors to revolutionize water quality monitoring. The PDMS-AuNPs/Au sensor not only provides accurate and fast COD measurements but also eliminates the drawbacks of conventional methods, such as the use of hazardous chemicals and complex procedures. This innovative approach opens new possibilities for real-time, on-site water monitoring in lakes, reservoirs, and other surface water bodies, contributing to better environmental management and public health protection.