16 1 may have to be different antigen 14 1 need not be the same antigen as that tested for provided it bonds to antibody 16 1 and blocks bonding of the tested antigen thereto moreover antigen 14 1 need not be pure provided a sufficient amount of appropriate antigen is present nonetheless antigen 14 1 is obtained in high pure quantities through selection by antibody 14 2 antibody 14 2 however must be pure to avoid the migration of enzyme 14 3 to region 18 accordingly a monoclonal antibody is preferred although affinity purified polyclonal antibodies may be used or affinity purified antibody to antigen 14 1 bond 24 must be pg 9 sufficiently strong to withstand thetest conditions whereby an insignificant amount of conjugate 14 2 14 3 freely migrates to region 18 referring to fig2 a strip as in fig1 contains three regions 24 26 28 in region 24 a coating contains antibody 24 1 bonded to enzyme 24 2 in region 26 antigen 26 1 is bonded to antibody 26 2 wherein antibody 26 2 is immobilized region 28 contains substrate 28 1 upon the addition of test solution containing antigen tested for conjugate24 1 24 2 is reconstituted whereby a conjugate is formed with the test antigen the conjugate passes through region 26 to region 28 whereby enzyme 24 2 reacts with substrate 28 1 to indicate the presence of test antigen in the absence of antigen in the test solution a conjugate 24 1 24 2 26 1 26 2 is formed by the immunological coupling between antigen 26 1 and immobilized antibody 26 2 and mobile antibody 24 1 thus enzyme 24 2 does not reach substrate 28 1 as in fig1 antibodies 24 1 26 2 may be like or.