FACTORS AFFECTING THE BACTERIAL CAPTURE EFFICIENCY OF IMMUNO BEADS: A COMPARISON BETWEEN BEADS WITH DIFFERENT SIZE AND DENSITY†

Abstract Biotinylated anti E. coli O157 antibodies were linked to streptavidin coated magnetic and polystyrene beads of different sizes and densities. These beads were then used to capture cultured E. coli O157:H7. Complexes formed between fluorescein-conjugated anti E. coli O157 antibodies and urease-conjugated anti-fluorescein antibodies further labeled bead-captured bacteria. The extent of the bacterial capture was related to the signal intensity of a light addressable potentiometric sensor (LAPS) that measured the pH changes associated with urease-catalyzed hydrolysis of urea. Under the conditions of applying the same amounts of biotinylated anti E. coli O157 antibody to beads, analyses of the capture kinetics indicated that heavier beads exhibited a better efficiency in capturing the target bacteria than that associated with the lighter beads of the same size. Furthermore, with the same density, larger bead diameters were more effective in capturing the bacteria. Since sedimentation volumes for the heavier and larger beads are greater than those of the lighter and smaller beads, more interactions with the target by the heavier and larger beads are expected. Consequently, the observation is in agreement with a hydrodynamic kinetic model that predicts the bacterial capture is controlled by the sedimentation motion of the beads.