in the membrane 14 this capture will give the fingerprint 62 swirls and whorls as is clearly shown in fig1 it should be noted that the test result for positive analytes is different in that there is no coloration while the negative areas show color this coloration of negative test areas and lack of coloration of positive test areas is used to prevent the subject being tested from reading the test results after the fingerprint has been made in that one normally assumes that a coloration test indicates positive rather than a lack of color in this example of latex entrapment with colloidal gold labelled antibodies as the color substrate antibodies and antigens bound to latex spheres were entrapped on the surface of a membrane the membrane must be low non specific protein binding and must have a smooth surface with consistent porosity 2 latexes 0 6 um idc polystyrene latex psl coated with goat anti mouse igg absorbed against human serum and hsa benzoylecgonine hsa be 3 colloidal gold conjugate 20 nm or 40 nm colloidall gold conjugated with goat anti mouse igg human absorbed 2 spot 40 ul of goat anti mouse igg psl 1 16 dilution into central well and 2 ul of hsa be psl 1 4 to 1 16 dilution in the appropriate number of test wells 3 invert on hydrophobic.