PCB-C⁴D Coupled with Activated Carbon-Barrier Paper-Based Microfluidic Sampling for Liquid Conductivity Detection with Improved Efficiency and Reduced Reagent Consumption

Liquid conductivity detection is a vital analytical technique for evaluating ionic composition in solutions, with broad applications in food safety, water quality monitoring, and agricultural analysis. This study introduces an innovative detection system that combines printed circuit board capacitively coupled contactless conductivity detection (PCB-C 4 D) with paper-based microfluidics modified by an activated carbon barrier. The barrier, integrated into the microfluidic channel through material engineering, effectively confines impurity particles while enabling capillary-driven flow through dual pathways: cellulose substrates and activated carbon. Leveraging activated carbon’s adsorption properties, the system achieves synergistic impurity removal, enhancing filtration efficiency and detection accuracy. Key optimizations included an activated carbon-to-cellulose ratio of 1.2:3 g and barrier dimensions (height: 0.4 mm; length: 3 mm), yielding a 60% reduction in sample consumption (8 μL), 4 s filtration speed, and high repeatability (RSD <0.86%, n = 6) with a detection limit of 4.98 μS cm⁻¹. A modular portable device was developed, integrating a detachable paper chip holder with PCB-C 4 D sensors for field applications. Practical robustness was validated through on-site analysis of complex matrices demonstrating rapid, reliable performance. This work advances paper-based conductivity detection by addressing filtration limitations in raw sample analysis, providing a cost-effective route to real-time in situ detection.