Finger-actuated microfluidic chip for chlorine and copper ion detection in water

Abstract

Ensuring a safe and clean water supply is essential for public health and environmental sustainability. The presence of contaminants, such as residual chlorine and copper ions, can pose significant health risks. Thus, developing rapid and reliable water quality monitoring techniques is essential. Conventional laboratory-based methods are highly accurate but depend on expensive instrumentation and trained personnel, making them unsuitable for on-site applications. To address this problem, this study presents a finger-actuated microfluidic chip integrated with a smartphone-based colorimetric analysis system for the rapid on-site detection of residual chlorine and copper ions in water. The PDMS/glass hybrid device is fully power-independent and utilizes only manual finger pressure to propel the samples and reagents through the microchannel network. The device incorporates a square-wave microchannel design to enhance passive fluid mixing within the confined microscale environment. The simulation and experimental results demonstrate an excellent agreement, with mixing efficiencies of 98.5% and 95.5%, respectively. For quantitative detection, a 3D-printed cassette is combined with a custom-developed smartphone application to capture and process RGB color data in real-time. The calibration curves constructed using residual chlorine (0.6–6 ppm) and copper ion (0.25–2 ppm) control samples exhibit excellent linearity, with coefficients of determination (R²) of 0.9902 and 0.9867, respectively. Moreover, verification trials performed using real environmental water samples reveal relative errors lower than 10.0% for residual chlorine and 9.6% for copper ions, confirming both the reliability and practical applicability of the proposed system. Overall, the portable, power-free microfluidic platform provides a cost-efficient and user-friendly tool for decentralized water quality monitoring, offering a practical solution for enhancing public health protection in regions lacking access to conventional laboratory infrastructure.