Figure 1: Principle for forward phase protein microarray (A) and reverse phase protein microarray (B). (A) Forward phase arrays immobilize a bait molecule such as an antibody designed to capture specific proteins representing a specific treatment or condition. The capture antibody is first affixed to the slide surface and then be used to capture antigens it recognizes when analytes (e.g., blood, cells, cell lysates, or some other biological specimen) are spread over the array. The bound analytes are detected by the labeling signal. (B) Reverse phase arrays immobilize the test sample analytes on a surface. A single antibody directed against the analyte of interest is applied for probing the array and the bound antibodies are detected by signal amplification.