Smart-PAD: A multi-channel mechanized approach for high-throughput paper-based colorimetric analysis: Determination...

Paper-based analytical devices (PADs) have gained widespread use in (bio)analytical colorimetric assays due to their portability, affordability, ease of use, and compatibility with point-of-care testing. Typical detection involves digital imaging or single/multi-channel light sensors to extract color data. However, these methods often require manual handling and operator intervention, leading to significant operator-dependent variability, reduced throughput, and limited reproducibility. Furthermore, these challenges limit the practical deployment of PADs for large-scale or automated analysis. The problem addressed here is the lack of fully automated, high-throughput PAD platforms capable of delivering precise, reproducible, and time-efficient colorimetric measurements with minimal human intervention.

We developed Smart-PAD, an automated analytical system integrating a 17-position 3D-printed sample wheel and an 8-channel digital light sensor (AS7341) controlled by an ESP-32 microcontroller. The platform performs sequential reflectance measurements every 19.4 s with precise timing and synchronization, achieving a relative standard deviation (RSD) of 3.2 % in tests with sunset yellow-impregnated PADs. We determined that a 15-min drying time is necessary for stable and accurate signals, ensuring measurement reliability. The system allows automated analysis of 17 spots, significantly improving throughput over manual procedures. Validation via the Berthelot reaction for ammonium quantification in fertilizer samples demonstrated high accuracy, reproducibility, and robustness in complex matrices under realistic analytical conditions. The platform's modularity and low cost also facilitate easy adaptation for diverse analytical applications.

Smart-PAD advances PAD-based colorimetric analysis by combining mechanized sample handling with multi-wavelength sensing technology, enabling high-throughput, precise, and reliable measurements. This platform offers a scalable, low-cost solution for automated, miniaturized analytical systems with broad potential applications across environmental monitoring, agricultural analysis, and biomedical diagnostics. Its innovation sets a new standard for automation and analytical performance in paper-based chemistry.