Liquid Imbibition in Paper Pathways: Rheology-Analyte Coupling Insights

ABSTRACT We experimentally investigate the effect of fluid rheology on wicking and analyte trapping in paper-based lateral flow assay using aqueous solution of sodium carboxymethyl cellulose (NaCMC). We develop a numerical framework, consistent with saturation-based flow model, to simulate the wicking phenomenon in paper-based porous strip using experimentally estimated effective viscosity of the solution. Increasing the NaCMC concentration leads to higher liquid entry pressure and greater flow heterogeneity in the paper strips. The numerically predicted liquid saturation level closely matches with our experimental data, obtained by using the Brook and Corey parameters. We perform Raman spectra analysis of the sample considered in this analysis, and find that higher NaCMC concentrations result in more stable hydrogen bonding because of the increased intensity of the hydroxyl group. We observe that he augmented intensity of hydroxyl group is capable of increasing the effective viscosity by an order of magnitude with NaCMC concentration. Consequently, we find that with increasing the concentration of NaCMC solution, the average wicking length and imbibition velocity decrease. Interestingly, the effective viscosity ratio appears to be less than unity at lower NaCMC concentrations at longer time instants. Diffusion and interception processes dominate total trapping efficiency, while particle trapping caused by inertial mechanisms is insignificant. We show that with higher concentration of NaCMC, the diffusion and overall theoretical trapping efficiency follow non-monotonic trend. Also, we found that the higher concentration of NaCMC in the sample reduces the critical axial location of the test line for an efficient reaction in the LFA