Lab on Paper

This study presents a facile and cost-effective cutting method for fabricating microfluidic paper-based analytical devices (µPADs). Three µPAD designs were developed, differing only in the coverage of the paper strip layer: one with a transparent sheet, one with adhesive tape, and one with no coverage. The imbibition behavior of deionized water through each µPAD design was compared, revealing the impact of evaporation, trapped gas, tortuosity, and layers on the imbibition process. A novel semi-empirical equation was formulated to model penetration length dynamics, utilizing regression analysis of experimental data. This approach distinguishes itself from previous studies by employing a unified equation applicable across all stages of dominant forces. Additionally, unlike earlier models that assume an infinite sample reservoir, this work considers a finite sample volume, thereby enhancing its practical applicability. As a result of the imbibition of 5 μL DI water through µPADs` channels, which were made of Whatman grade 42 filter paper with a width of 2 mm (±0.05), the final imbibition length was measured as 29.9, 28.8, and 24.1 mm, respectively for each type as mentioned before. Furthermore, the coefficient of determination (R²) of 0.9999 for the semi-empirical equation indicated a superior fit for the first µPAD type. Finally, the optimized µPAD design was selected for experiments involving six concentrations of methyl orange to examine the influence of concentration on both the equation constants and the final imbibition length. The findings presented in this study advance microfluidic paper-based analytical device technology and offer valuable insights into fluid behavior within porous media.