Tamm-Horsfall (THP)-specific antibodies are conjugated with blue latex beads and incorporated beneath the sample window. Another THP-specific antibody is fixed at the test line. If THP is present in the sample, it will form an antigen-antibody-colloidal gold complex upon deposition. These complexes react with the antibodies fixed at the test line to form a visible blue line indicating the presence of THP, and therefore, urine. Semen – Human semenogelin-specific antibodies are conjugated with colloidal gold and incorporated beneath the sample window. An anti-semenogelin antibody is fixed at the test line. If human semenogelin is present in the sample, it will form an antigen-antibody-colloidal gold complex upon deposition. These complexes react with the antibodies fixed at the test line to form a visible red line indicating the presence of human semenogelin, and therefore, human semen. See also Forensic serology Luminol References Further reading Forensic techniques