Computational and Experimental Techniques to Analyze Antibody-Analyte Transport and Reaction in Microchannels
The goal of this research is to investigate computational and experimental techniques to effectively analyze microscale fluid dynamics, transport, and mixing of an analyte-antibody system. This work is applicable to the development of an in-plane, passive mixer component of a miniature antibody-based sensor suitable for environmental monitoring, food testing, and medical diagnostics. The computational methods allow the efficient evaluation of microchannel designs to enhance analyte-antibody binding, which may reduce the time and cost required for experimental trials. We describe a computational algorithm to solve the governing equations for microscale fluid flow and transport in complex 2-D domains created through a graphical user interface. We implement the particle strength exchange method to solve the convection-diffusion-reaction equations, coupled to the boundary element method to compute the velocity field from the steady state Stokes equations. We validate the numerical methods by comparison to analytical and finite element method solutions. Because the chosen methods require no internal mesh, our algorithm provides an efficient alternative to grid-based methods when solving transport in complex geometries with internal obstacles. We characterize two fluorescein-antibody clones through competitive ELISA experiments and demonstrate the quenching effect of the antibodies with a fluorescence spectrophotometer. We describe a microchannel flow system to image the quenching of fluorescence by the antibody when fluorescein and fluorescein-antibody solutions are injected into separate inlets of the microchannel. We correlate the fluorescence intensity of microscope images of fluorescein flowing through the microchannel to concentrations of fluorescein to establish a calibration curve. This system provides a method to visualize and quantitatively analyze the mixing and reaction in a microfluidic device. We test the numerical methods by comparing the experimentally determined fluorescein concentration to the outlet amount numerically predicted by the computational model under identical conditions and find good agreement between the two fluorescein concentration profiles. We complete the transport-reaction computation in a set of microchannels with cylindrical obstructions. We find that decreasing the channel width and increasing the fluid path length by placing the obstruction on the walls is more effective than placing free-standing obstructions within the channel to enhance the fluorescein and fluorescein-antibody reaction.