Dynamic arraying of microbeads for bioassays in microfluidic channels

This paper proposes a new dynamic mode of generating bioanalytical arrays in microfluidic systems, based on ultrasonic trapping of microbeads using acoustic forces in standing waves. Trapping of microbead clusters in an array format within a flow-through device is demonstrated for the first time using a device with three integrated ultrasonic microtransducers. The lateral extension of each trapping site was essentially determined by the corresponding microtransducer dimensions, 0.8 mm x 0.8 mm. The flow-through volume was approximately 1 μ l and the trapping site volumes about 100 nl each. The strength of trapping was investigated, showing that 50% of the initially trapped beads were still trapped at a perfusion rate of 10 μ l/min. A fluorescence based avidin bioassay was successfully performed on biotin-coated microbeads trapped in the flow-through device, providing a first proof of principle of the proposed dynamic arraying concept. The dynamic arraying is believed to be expandable to two dimensions, thus, with a prospect of performing targeted and highly parallel protein analysis in microfluidic devices.