A novel fluoroimmunoassay method using bacterial magnetic particles for the highly sensitive detection of bacteria has been developed. Fluorescein isothiocyanate (FITC) conjugated monoclonal anti-Escherichia coli antibody was immobilized onto bacterial magnetic particles (BMPs) using a heterobifunctional reagent, N-succinimdyl 3-(2-pyridyldithio)propionate (SPDP). E. coli cells were reacted with FITC-antibody-BMP conjugates for 15 min in an inhomogeneous magnetic field which enhanced aggregation. The cell/BMP complexes sedimented, causing relative fluorescence intensity of the solution to decrease with increasing microbial cell concentration. A linear relationship was obtained between the relative fluorescence intensity and cell concentration in the range of 102-106 cells/mL. Selectivity of this detection system was satisfactory. Monoclonal antibody immobilized on BMPs was also applied to the specific removal of E, coli from the bacterial suspension.
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