Bead packing and release using flexible polydimethylsiloxane membrane for semi-continuous biosensing

The continuous or semi-continuous biosensing of systemic inflammatory responses is important both during and after cardiopulmonary bypass (CPB) procedures. A bead packing and release method, which is able repetitively to capture and release receptor-coated beads within microfluidic channels, is herein advanced for use in semi-continuous biosensing. The receptor-coated beads are compacted and concentrated at specific locations in the device using an elastomeric valve. This concentration creates a localized bioreactor in which the binding of the antigen with the functionalized beads can be made more effective. After the reaction and detection have taken place, the beads can be released and a new assay carried out. We demonstrated the operation of our device using streptavidin-coated beads and biotin-4-fluorescein (B4F). The high sensitivity of the device allows it to detect a B4F concentration of 50 pg/mL after an incubation time of 5 min. We also tested our device in the semi-continuous immunoassay of interleukin (IL)-6, which is one of the proinflammatory cytokines. The assay demonstrated the linear dependence of the intensity of fluorescence at concentrations of IL-6 from 10 to 250 pg/mL, which is a physiologically important range for CPB procedures.