Formation of hexagonal monolayers by flow of bead suspensions into flat microchambers
To realize a highly parallel optical detection in bead-based bioanalytical assays, we investigate the hydrodynamic aggregation of bead suspensions in a hexagonally perodical monolayer by a pressure-driven flow through a microfluidic structure. This device consists of one inlet channel connected to a shallow chamber with a depth that only slightly exceeds the diameter of the beads, the flow leaves the chamber via outlet channels possessing a depth smaller than a bead diameter. This way the outlets act as barriers to the beads and force them to accumulate in the chamber. Benchmarking different chamber and outlet designs we found an optimum filling behavior for a rhombus-like aggregation chamber connected to a single outlet channel at the same width as the chamber. Here, the aperture angle of 60° fosters hexagonal aggregation patterns which leads to the highest packaging density. Reproducible filling ratios of more than 94 % have been achieved. The rhombus-like chamber also shows the smallest increase of the hydrodynamic resistance during filling and the best rinsing behavior which allows to minimize the volume of washing detergents used for a bioassay. Zones of accumulated beads redistribute the hydrodynamic flow through the device during the filling process. CFD-simulations, embedded in an iterative master-routine, are caried out to describe the complete process of filling and to assist the process of design optimization.