Luminescent quantum dot nanoparticles have emerged as a highly effective alternative to organic fluorescence probes in a variety of applications employing the use of immunoconjugates. In the present study, we have successfully used quantum dot technology for the immunofluorescent detection of intracellular stages of Toxoplasma gondii in a CV-1 mammalian cell line. This assay will allow us to investigate the question of whether selenium and other antioxidants have a direct impact on the intracellular cycle of the parasite. A Lab-Tek cell culture system was used to determine optimal concentrations of primary and secondary antibodies. Infected CV-1 monolayers were fixed in 4% formalin and cell membranes were permeabilized with detergent prior to blocking and immune-labeling. The use of a mouse anti-T. gondii primary antiserum followed by quantum dot--conjugated secondary antibody (Goat anti-mouse IgG) resulted in a punctuate, intensely bright fluorescent labeling of intracellular tachyzoite stages with no evidence of photobleaching or fading. In addition, the application of cover slips using Cryoseal Mounting Media 60, allowed for the long term storage of stained slide preparations
