Numerical Analysis on 3D Microfluidic Paper Based Analytical Device

Abstract

Paper-based microfluidics are microfluidic devices that consist of a series of hydrophilic cellulose or nitrocellulose fibers that transport fluid from an inlet through the porous medium to a desired outlet or region of the device, by means of capillary action. Paper is abundant and compatible with many chemical/biochemical/medical applications, it is easy to use, disposable, equipment free, and its high surface area improves detection limits for colorimetric method, its ability to store reagents in active form within the fiber network. It provides a novel system for fluid handling and fluid analysis for a variety of applications including health diagnostics, environmental monitoring as well as food testing. It has been used from spot tests for metals and paper chromatography to lateral flow immunoassays and later now as multilayered (μPADs). Different technologies has been adopted in past for fabrication of (μPADs). The fundamental principle underlying these fabrication techniques is to pattern hydrophilic-hydrophobic contrast on a sheet of paper in order to create micron-scale (i.e., hundreds to thousands of micrometers) capillary channels on paper. Their widespread adoption has been limited by slow flow rates of fluid passing through it, shelf life of enzyme/reagent stored on paper, coffee ring effect in which there is non-uniform distribution of reagent due to hydrophobic boundary, theoretical modeling which accurately depicts behavior of fluid flow through multilayered μPADs considering all design parameters, non-homogenous paper causes anisotropic properties. In counter to that in this present work, numerical analysis of impact of various design parameters on the performance of single and multilayered paper based microfluidic analytical devices (μPADs) is performed, in order to find effect of different design parameters on velocity of fluid e.g. porosity, permeability, capillary angle, gap height, surface tension, dynamic viscosity, paper thickness, paper width etc. Based on the results of numerical analysis, it is concluded that permeability, gap height, interfacial tension, paper thickness are directly proportional with the velocity of fluid and the remaining design parameters dynamic viscosity, capillary angle are inversely proportional with the velocity of fluid, porosity doesn’t affect velocity value. Whatman filter paper grade 4 is recommended for single layered and multilayered microPADs, because velocity of fluid is found to be 1.3 mm/s in case of single layered microPADs. Maximum gap height that is beneficial for velocity enhancement in multilayered microPADs is 400 μm. Optimum value of paper width is found to be 0.02m for enhanced velocity. Based on these findings one can manufacture paper material of certain desired properties to get favorable results and can also fabricate multilayered microPADs while keeping gap height behavior under consideration