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Optimization of Micro-Fluidic Network Geometries for Micromosaic Immunoassays

Nicholas S. Lynn1, Brian Murphy2, Charles S. Henry2, and David S. Dandy1. (1) Department of Chemical and Biological Engineering, Colorado State University, 100 Glover building, Fort Collins, CO 80523, (2) Department of Chemistry, Colorado State University, Fort Collins, CO 80523

Protein patterning is ubiquitous in the creation of sensing motifs that rely on receptor-ligand binding for selectivity. Autonomous micro-fluidic networks (µFNs) have the potential to greatly aid in the development of simple, robust methods for deposition of biological capture agents onto a solid substrate. Unfortunately, µFN-based micro-immunoassays involving multiple binding regions suffer from the formation of an analyte depletion layer adjacent to the micro-channel floor where binding occurs. As a result, the time required to achieve equilibrium binding states for all binding surfaces is strongly dependent on both the flow conditions within the micro-channel and the geometries of the channel itself. These systems exhibit a critical flow rate (characterized by the linear velocity) below which the system becomes diffusion limited and assay times grow well beyond practical limits. For optimal µFN assay times that utilize minimal sample volumes, there is a delicate balance between the absolute flow rate through the system and the overall time in which that flow rate can be maintained. Here we report a simple method to control the flow conditions in autonomous µFNs by manipulation of simple geometric and operational parameters in order to both minimize assay time and required sample volume. The system is shown to be very flexible, providing precise control over the flow conditions over a wide rage of flow rates, utilizing only a micropipette and simple soft lithographic methods.