Immunomagnetic separation (IMS) is a rapid, technically simple, specific and efficient method that can be used for isolation/concentration of target bioagents directly from real-world samples without any need of centrifugation or filtration. We demonstrated that immunomagnetic nanobeads are advantageous over microbeads because of their higher capture efficiency, no need for mechanical mixing, and minimal sample preparation. The nanobeads present a minimum capture efficiency of 94% for Escherichia coli O157:H7 ranging from 1.6 x 101 to 7.2 x 107 CFU/ml with an immunoreaction time of 15 min without any enrichment .

Comparison of the capture efficiency of immunomagnetic nanobeads (145 nm) and microbeads (2.8 mm) for E. coli O157:H7. Immunoreaction time, 30 min.

Capture efficiency of immunomagnetic nanobeads (145 nm) against Escherichia coli O157:H7 of different concentrations as a function of immunoreaction time.

M. Varshney, L. Yang, X.-L. Su, Y. Li. 2005. Magnetic nanoparticle-antibody conjugates for the separation of Escherichia coli O157:H7 in ground beef. J. Food Prot. (in press).