Moving the solid phase: a platform technology for cartridge based sandwich immunoassays

We report on a cartridge based platform for complex immunoassay formats that allows for flexible adaption of individual steps. It is a sample-to-answer system which is quantitative as well as sensitive. The target molecules are detected through a magnetic bead-based fluorescence sandwich immunoassay. The beads both constitute the solid phase for immobilizing capture molecules and are used for magnetic field activated incubation. The injection molded cartridge comprises several chambers separated by capillary valves. Chambers contain the assay reagents, through which the beads are manipulated via externally applied magnetic fields. Active incubation is made possible by assembling the beads into microstirrers and systematically scanning through a chamber. The beads are transported by focusing them to form an aggregate which subsequently is dragged through the valves. Once the aggregate enters a chamber, it is re-dispersed and magnetic actuation is used to re-assemble the beads into microstirrers. The assay protocol involves an incubation of sample with antibody coated magnetic beads, followed by steps for washing or separation, labeling with fluorescent detection antibody and finally fluorescence detection. An interleukin-8 assay served as a model for evaluating the system and a concentration as low as 5 pg/mL (0.625 pM) was successfully detected. The platform shows potential to be developed into a diagnostic tool to be used in a point-of-care testing (PoCT) environment.