Comparison of immunomagnetic beads coated with protein A, protein G, or goat anti-mouse immunoglobulins. Applications in enzyme immunoassays and immunomagnetic separations.

Immunomagnetic beads were prepared using either protein A (PA) or protein G (PG) coupled to magnetic beads for binding antibodies at their Fc region. The performance of these beads was compared with commercially available beads coated with goat anti-mouse (G alpha M) immunoglobulins. Both the PA- and PG-beads possessed a higher binding capacity than the G alpha M-beads for the monoclonal antibodies tested, although, PA bound weakly with some IgG1 antibodies. PA-beads were compared with G alpha M-beads in a magnetic enzyme immunoassay for the detection of mouse immunoglobulins as an alternative to a conventional capture ELISA. The magnetic enzyme immunoassay was characterized by a detection time of less than 60 min and a linear assay range from 5-10 to 500 ng/ml for G alpha M-beads and 5-10 to 1000 ng/ml for PA-beads. The capture ELISA was linear from 10 to 250 ng/ml. For immunomagnetic separation of Salmonella with immunomagnetic beads, PA-beads were superior to both PG- and G alpha M-beads. For specific isolation of bacteria from heterogeneous suspensions by immunomagnetic separation, PA- and PG-beads are preferable since G alpha M-beads crossreact with bacteria possessing proteins with Fc-binding activity.