Monoclonal antibodies are used in home pregnancy test kits.Early on in pregnancy the placenta produces the hormone hCG (human chorionic gonadotropin) which can be found in the mother's urine.Mobile monoclonal antibodies are linked to coloured particles. Immobile monoclonal antibodies on a test strip will bind to the mobile antibodies if they are bound to hCG.If hCG is present in the urine it binds to the mobile monoclonal antibodies. The hCG-antibody-colour complex moves along the strip until it is trapped by the immobilised antibodies creating a coloured line.