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. Threedimensional, 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.

Hot embossed polyethylene through-hole chips for bead-based microfluidicdevices

“…These models agree well with confocal imaging. (Thompson and Bau 2012) Similarly, our group has shown, through simulations and experimental evidence, the preponderance of porous beads as highly sensitive sensing elements due to the existence of internal convection inside porous beads. (Chou et al 2012) These bead-based devices have shown potential as highly sensitive, robust sensing elements for rapid detection of biological agents.…”

Transport of biomolecules to binding partners displayed on the surface of microbeads arrayed in traps in a microfluidic cell

“…Another method for constructing a microbead array/probe library in a microfluidic cell is to place the functionalized microbeads in shallow wells arrayed at the bottom of the channel, and then place the channel top on the microbead array. [37][38][39][40] The height of the channel is the same size as the microbead diameter, so that the channel top holds the microbeads in place. The binding rate in this geometry approaches the idealized case of an unobstructed microbead in the channel for all Pe, but the microbead array assembly is undertaken ex-situ, which is more demanding than the in-situ hydrodynamic entrapment studied here.…”

“…[34][35][36], the binding of target to microbeads captured in traps has received very limited attention. Bau et al [37][38][39][40] studied the geometry of microbeads sandwiched between the top surface of a flow channel and a shallow well at the bottom of the channel (the microbeads were preassembled in the shallow wells before closing the cell), and obtained solutions for the target concentration on the microbead surface as a function of the stream velocity and target-probe kinetic rate constants. These simulations represent approximately the idealized case of unobstructed microbeads.…”

Porous Bead-Based Diagnostic Platforms: Bridging the Gaps in Healthcare

“…Thompson et al developed a model in an attempt to understand the effects of analyte diffusion coefficient, flow rate, and capture probe density on the kinetics on bead surfaces [131]. Further, the combination of confocal microscopy and computational simulations helped to define the spatial and temporal distribution of bound biotinylated quantum dots on streptavidin-coated beads [132]. …”