Integrated Capillary-Flow-Driven Paper-Based Microfluidic Sensor and ChromaSense Lab Mobile Analytical Platform for Quantitative Detection of 6PPD in Stormwater Runoff

Abstract N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) is a widely used tire anti-degradant that is continuously released into the environment through tire wear and serves as the primary precursor to 6PPD-quinone, a transformation product associated with aquatic toxicity. Current determination of 6PPD primarily relies on laboratory-based chromatographic techniques requiring expensive instrumentation, specialized facilities, and trained personnel, limiting their suitability for rapid field deployment. Here, we report an integrated smartphone-assisted capillary-flow-driven paper-based microfluidic platform for quantitative detection of 6PPD in stormwater and roadway runoff. To the best of our knowledge, this is the first paper-based microfluidic platform developed for 6PPD analysis. The platform combines a capillary-flow-driven colorimetric sensor with ChromaSense Lab, a smartphone-based analytical platform that integrates image acquisition, flexible region-of-interest selection, quantitative color analysis, calibration generation, concentration prediction, and data export into a unified mobile workflow. Under optimized conditions, the sensor exhibited a linear response over the concentration range of 0−400 ppm with limits of detection and quantification of 9 ppm and 30 ppm, respectively. Calibration curves generated using ChromaSense Lab demonstrated excellent agreement with conventional ImageJ analysis (R2 = 0.993 and 0.995, respectively), validating the accuracy of smartphone-based quantification. The platform showed minimal interference from common inorganic ions and surfactants, maintained stability for at least four weeks under refrigerated and frozen storage conditions, and achieved recoveries generally within 80−120% with relative standard deviations within 10% in tap water, river water, and lake water samples. The sensor also achieved an AGREE greenness score of 0.81, demonstrating strong adherence to green analytical chemistry principles. By combining the first paper-based microfluidic sensor for 6PPD with a general-purpose smartphone analytical platform, this work establishes a rapid, portable, and user-friendly framework for decentralized screening of tire-derived contaminants in stormwater and roadway runoff. Although demonstrated for 6PPD detection, ChromaSense Lab was designed as an analyte-independent analytical platform and can be readily adapted to a broad range of paper-based, lateral flow, and other colorimetric sensing applications.