BRIDGING LAB AND FIELD: CAPILLARY MICROFLUIDICS FOR RAPID, LOW COST, CITIZEN-BASED POLLUTION MONITORING

Abstract

There is growing interest in how human activities impact the environment and, in turn, human health. Pollution from point and non-point sources can cause lasting environmental harm, but we lack important information on contaminant distribution. As such, a major gap in addressing this issue is the lack of fast, simple, inexpensive testing solutions. Microfluidic devices can offer a practical solution, enabling fast and affordable testing. Easy-to-operate tools can be used by citizen scientists to test pollution levels, expanding data collection efforts. This reduces the need for frequent visits by professional scientists and can lead to substantial cost savings. This dissertation highlights different capillary-based microfluidic platforms I have developed to overcome the key limitations of traditional sensing platforms for contaminant detection, bridging the “lab-to-field” gap for citizen-based environmental monitoring.Building on this foundation, a series of capillary flow–driven microfluidic platforms are developed to overcome key limitations of traditional paper-based analytical devices, including slow transport, reliance on precise volume handling, and limited sensitivity. A hollow capillary-driven architecture was first introduced to enable rapid analyte transport and homogeneous signal generation, allowing for the detection of heavy metals such as Ni(II), Cu(II), and Fe(III) within seconds using a simple dip-and-read format. This approach demonstrated that decoupling fluid transport from in-plane paper wicking can significantly improve assay speed and usability for point-of-need applications. To address sensitivity limitations inherent to colorimetric detection, a low-cost preconcentration strategy was developed and integrated with the capillary-driven platform. This system enabled multiplexed detection of seven heavy metal ions at low parts-per-billion levels using a simple Fill–Fold–Photo workflow and smartphone-based analysis. The platform achieved detection limits meeting or exceeding regulatory guidelines while maintaining portability and user-friendly operation, demonstrating its suitability for field deployment. The scalability and real-world applicability of these platforms were further demonstrated through the development of a robust phosphate sensor designed for citizen-based environmental monitoring. By combining fast-flow microfluidic design with improved reagent stabilization, the system enabled accurate and reproducible measurements under ambient conditions. Large-scale deployment of more than one thousand sensors across multiple continents enabled high spatial and temporal resolution mapping of phosphate contamination, highlighting the potential of these technologies for decentralized environmental monitoring. Finally, the scope of capillary-driven microfluidics was extended to analytes requiring chemical transformation prior to detection. A paper-based microfluidic platform integrating on-chip photochemical nitrosation was developed for the detection of N-nitrosodimethylamine (NDMA), enabling a complete photochemical–colorimetric workflow within a portable format. This approach demonstrates the versatility of capillary-driven systems and their potential to expand beyond direct detection to more complex analytical challenges.