Objective    To establish a new double-antibody sandwich ELISA to detect the antigen AP33 (a 33 kDa adhesive protein) of

Trichomonas vaginalis

based on the quantum dots and magnetic beads.     Methods    After BALB/c mice were immunized by AP33

the multiclonal antibodies in the antiserum was conjugated with the quantum dots and magnetic beads by carbon diimine crosslinking method respectively. Then the antibodies combined with magnetic beads were coated to microwell of plate as capturing antibody

and the antibodies bound to quantum dots were regarded as the marked antibody which can be directly observed under fluorescence microscope and quatitated by spectrofluorometry. The specificity and sensitivity of our established system were investigated.     Results    AP33

was successfully detected at the concentration as low as 50 ng/ml by this with-filling method. No crossreaction was observed when this system was used to detect

Trichomonas vaginalis

and other common bacteria in the vagina. The accuracy was 88% and the specificity was 90%.     Conclusion    This new double-antibody sandwich ELISA to detect

Trichomonas vaginalis

is successfully prepared and of sound specificity and sensitivity.