Overprint immunoassay using protein A microarrays.

The ability to perform microarray-based immunoassays without the need for wells or other fluid barriers were demonstrated. Both contact and noncontact microarray printing technology is used to prepare spotted arrays of analyte binding sites, as well as, to deliver samples, secondary antibodies and other signal development reagents directly to these sites in a parallel fashion are called as overprint immunoassays. A micro-ELISA is demonstrated based upon the use of Protein A as a universal microarray. All components of the assay (capture antibody, antigen, and signal development reagents) were site-specifically dispensed in parallel fashion to the surface in nanoliter volumes. This represents a 1000-fold reduction in reagent consumption from that used in a conventional 96-well microtiter plate assay. Overprinting nanoliter volumes directly onto 200-300 microm spots yields similar levels of sensitivity achieved with the bulk dispensing of microliter volumes into wells.