Porous bead-based microfluidic assay: theory and confocal microscope imaging

Abstract

Functionalized, porous microbeads provide large surface area to volume ratios, allowing the capture of relatively large quantities of target molecules from complex solutions and, thus, facilitating high-sensitivity assays. While in recent years the interest in bead-based assays has been growing, only a few studies focus on mass transfer in the bead’s interior and on the binding kinetics of functionalized, porous beads. In this study, streptavidin-coated, porous agarose beads are controllably positioned within a microfluidic conduit. Biotinylated quantum dots are pumped through the conduit and used as labels to monitor target analyte binding to the beads. Confocal microscopy techniques are employed to image the concentration of the bound quantum labels as a function of position and time. Three-dimensional, finite element simulations are carried out to model the mass transfer and binding kinetics within the beads. Key thermophysical properties, such as the reduced diffusivity of the quantum dots in the agarose matrix, are determined experimentally. Experimental observations are critically compared and favorably agree with theoretical predictions. The theoretical models provide a useful tool to better our understanding of the phenomena involved and to predict how various parameters affect microbead reaction kinetics and biosensor performance.