A layer-by-layer paper-based analytical device with controlled interfacial gaps for rapid determination of dissolved inorganic carbon in water.

Paper-based analytical devices (PADs) are attractive for point-of-need water analysis because of their low cost and operational simplicity. However, slow fluid transport often limits their analytical throughput. Here, we report a layer-by-layer PAD incorporating controlled interfacial gaps to enhance capillary-driven transport for the determination of dissolved inorganic carbon (DIC) in water. The device employs distance-based colorimetric detection using an acid-base system with bromocresol green (BCG) and was benchmarked against a laminated configuration fabricated from the same Whatman grade 4 paper. The layer-by-layer architecture reduced the colorimetric response time from 18 to 2.5 min while achieving limits of detection and quantification of 0.30 and 0.92 mg L-1, respectively. Analysis of bottled mineral water samples showed good agreement with a reference potentiometric titration method, with relative errors below 7%. These results demonstrate that controlled interfacial engineering can be effectively integrated into distance-based PADs to accelerate analysis without modifying the sensing chemistry, providing a simple and low-cost approach for rapid on-site DIC determination.