Visual Quantitation of Copper Ions Based on a Microfluidic Particle Dam Reflecting the Cu(II)-Catalyzed Oxidative...

Due to the use of copper water pipes and the discharge of industrial wastewater, contamination of copper ions in drinking water has become a severe hazard globally. To routinely check water safety on a daily basis, easy-to-use platforms for quantitative analysis of trace amounts of copper ions (Cu²⁺) in drinking water is needed. Here, we report microfluidic particle accumulation integrated with a Cu(II)-catalyzed Fenton reaction for visual and quantitative copper ion detection. Microparticles (MMPs) and polystyrene microparticles (PMPs) are connected via a single strand DNA, MB155. However, when Cu²⁺ is present, MB155 is cleaved by hydroxyl free radicals (•OH) produced from Cu²⁺/hydrogen peroxide (H₂O₂) Fenton reactions, causing an increased amount of free PMPs. To visually count them, the particle solution is loaded onto a microfluidic chip where free MMPs and MMPs-MB155-PMPs can be collected by the magnetic separator, while the free PMPs continue flowing until being accumulated at the particle dam. The results showed a good linear relationship between the trapping length of PMP accumulation and the Cu²⁺ concentration from 0 to 300 nM. A limit of detection (LOD) of 70.1 nM was achieved, which is approximately 449 times lower than the 2 × 10³ μg·L^-1 (~31.5 μM) required by the World Health Organization (WHO). Moreover, the results showed high selectivity and good tolerance to pH and hardness, indicating compatibility for detection in tap water, suggesting a potential platform for the routine monitoring of copper contamination in drinking water.