Fig. 4.

(A) Bacterial titration. The concentration of L. monocytogenes or E. coli was varied, whereas the particle concentration was fixed at 0.05 relative to the stock suspension. (B) Particle titration. The particle concentration was varied, whereas the bacterial concentration was fixed at 10⁸ per ml L. monocytogenes or E. coli. The magnetic relaxation signal of each sample was fit to a combination of logarithmic and exponential functions; the logarithmic amplitude of each sample is displayed. A two-antibody model, described in the text, was used to fit the L. monocytogenes data.