By using the Ab-Match Universal kit in combination with the Ab-Match AsseMBLIy kit for target protein, the sandwich ELISA system is build. The capture antibody is coated on a 96-well microplate. Standards or samples are added to the microwells, allowing target protein to bind to the capture antibody in proportion to the concentration of target protein in the samples. After wash unbound target protein, detection antibody is added and attaches to the target protein bound to coated antibody. After washing away all unbound detection antibody, initiate the substrate reaction. After substrate reaction, add the stop solution to the microwell plate. Then the relative amount of target protein bound in each well can be determined from the yellow color using a microplate reader. The concentration of target protein in each sample can be obtained by comparing the optical density (OD) of the sample to the OD of the standards on the plate.