Bead Hopper Loads Up Microfluidic Devices

Functionalized polymeric beads are commonly used as substrates for high-throughput syntheses and analyses carried out in microwell plates or vials. Their small size also makes the beads a perfect match for flow-through microfluidic systems, but loading them into the devices before they fall out of suspension is difficult. Brian M. Paegel, Alexander K. Price, and Andrew B. MacConnell of Scripps Research Institute Florida have now turned this tricky sedimentation problem to their advantage for loading bead libraries (Anal. Chem. 2014, DOI: 10.1021/ac500693r). They first construct a “bead suspension hopper” from a modified pipette tip. After filling the hopper with a suspension of beads, they allow the beads to settle in the tip, from which they are dispensed into a fluid stream—more than 100,000 beads can be dispensed in a few hours. After the beads are released, they are encapsulated in oil droplets, which function as individual reactor cells. The researchers demonstrated the device with an HIV-1 protease activity assay and with a protein evolution experiment. “The suspension hopper should effectively remove any barriers to using suspensions as sample inputs, paving the way for microfluidic automation to replace robotic library distribution,” the researchers write.