Ultrasensitive magnetic particle-based immunosupported liquid membrane assay

A magnetic particle-based immuno-supported liquid membrane assay (m-ISLMA) based on chemiluminescence detection of a horseradish peroxidase-labeled hapten tracer that allows sample cleanup, analyte enrichment, and detection in a single analysis unit has been developed. Antibodies were immobilized on magnetic beads, and their position in the acceptor was controlled by two alternating opposing electromagnetic fields generated by a voltage applied to either of two electromagnets placed below and above the acceptor channel of the supported liquid membrane unit. The influence of antibody bead dilution in the acceptor was investigated and found to follow the ISLM theory, that is improved enrichment and sensitivity with increasing antibody concentration. Two different extraction procedures were investigated: procedure 1 (m-ISLMA-P1), which keeps the antibody beads trapped at the bottom of the acceptor during the entire analysis process; and procedure 2 (m-ISLMA-P2), which keeps the antibody beads dispersed and in motion in the acceptor phase during the extraction process, m-ISLMA-P2 resulted in 2000 times improved enrichment of simazine and a more than 3 orders of magnitude better limit of detection ([LOD.sub.10%].) (1.29 x [10.sup.-5] [micro]g [L.sup.-1]) than for m-ISLMA-P1 (2.00 x [10.sup.-2] [micro]g [L.sup.-1]) and corresponding microtiter plate magnetic particle-based ELISA (m-ELISA, [LOD.sub.10%] 1.30 x [10.sup.-1] [micro]g [L.sup.-1]). m-ISLMA-P2 and m-ELISA were further applied for the extraction and analysis of simazine-spiked surface water and fruit juice, finding no evidence for matrix influence for the former method; however, indications that trace amounts (nanograms per liter) of simazine or specific cross-reactants were present in both samples.