Sensitive detection of biotoxoids and bacterial spores using an immunomagnetic electrochemiluminescence sensor

Extremely sensitive detection of various biotoxoids and bacterial spores using the commercial ORIGEN analyzer was achieved by capture on antibody-conjugated micron sized magnetic beads (MBs) followed by binding of ruthenium (II) trisbipyridal chelate (Ru(bpy)2+3-labelled reporter antibodies. Immunomagnetically captured target materials were collected on a magnet. Electrochemiluminescence (ECL) was evoked from the Ru(bpy)3(2+)-tagged reporter antibodies by application of an electrical potential. Femtogram sensitivity levels were obtained for all biotoxoids tested including botulinus A, cholera beta subunit, ricin and staphylococcal enterotoxoid B by this immunomagnetic (IM)-ECL approach. An IM-ECL assay for Bacillus anthracis spores yielded a detection limit of at least 100 spores. The ECL signal was a function of analyte quantity over several orders of magnitude, but the immunological 'hook' effect at high antigen loads made quantitation impossible over a broader range. All assays were performed with a maximum combined incubation and assay time of approximately 40 min. This work demonstrates the extreme sensitivity of the IM-ECL approach for soluble and particulate antigens.