Ultrasensitive Detection of Macromolecules in Water Via Flowing Nanoparticles on a Microchip

Synthetic, natural, and biological macromolecules are ubiquitous in aquatic environments, affecting industrial processes such as filtration and posing ecological risks even at trace levels. Here, exploiting particle-polymer interactions under flow, we report a microfluidic platform for ultrasensitive monitoring of macromolecules in water. Fixed obstacles act as "collectors" enriching macromolecules, while injected micro/nanoparticles serve as "detectors" binding to those accumulated at the surface. The resulting ordered particle accumulation is visualized to assess macromolecule contamination using a standard microfluidic setup without additional assays or specialized modules. Quantitative analyses show well-calibrated concentration-intensity relationships, with parts-per-billion-level detection limits and subminute response times. Transitions in accumulation patterns under varying macromolecular properties further allow substance identification. Compared with existing methods, our approach demonstrates superior performance across sensitivity, selectivity, efficiency, and cost. The platform provides an alternative for water quality assessment and enables broader applications such as capture of micro/nanoplastics.