Figure 1: Different platforms for planar-form of antibody arrays. (A) The sandwich method requires an immobilized capture antibody and a labeled, insolution detection antibody. (B) The competitive method relies on competitive binding between the analyte and a labeled antigen. (C) The direct-label method requires the label being attached to the analyte itself. (D). The label-free method relies on an inherent property of the analyte (such as mass per unit area or surface plasmon resonance) to produce a signal.