Capillary flow-driven paper-based microfluidic sensor for NDMA detection in water

N-Nitrosodimethylamine (NDMA) is a genotoxic nitrosamine that is commonly found in water due to its ready formation from commonly available precursor compounds. Routine monitoring of NDMA in water is challenging due to the need for complex sample preparation and instrumentation. Here, we propose the first example of an NDMA assay on a paper-based microfluidic platform. Moreover, it is the first study to integrate the required photochemical nitrosation reaction directly on-chip, enabling a complete photochemical-colorimetric workflow. The device is constructed with hollow PET capillary channels, double-sided adhesive, and glass fiber/paper pads with immobilized reagents, enabling sample analysis by simply dipping the device into water. On-chip detection of NDMA with sodium 1-naphthol-4-sulfonate is followed by Fe²⁺- and Co²⁺-based complexation, producing complementary green and red chromogenic signals. Its user-friendly dip-and-fold operation facilitates on-site, rapid, and high-frequency monitoring. The Fe²⁺- and Co²⁺-based channels provide linear detection ranges of 0-100 ppm and 0-30 ppm, with limits of detection of 4 ppm and 1.5 ppm, respectively. Interference studies, proper masking strategies, and dual-channel readout ensured high selectivity, while stability tests demonstrated excellent device stability over four weeks. Spike recovery experiments in tap, river, and lake water showed consistent recovery performance with RSD < 10%. This sustainable platform costs less than $0.2 per device, is compatible with smartphone-based readout, and offers a practical alternative to conventional analytical techniques. The findings presented here open possibilities to expand on-chip photochemical reactions in paper-based and other microfluidic systems for the detection of a broader range of contaminants.