At present, it takes technicians a few days to incubate and determine the existence of bacteria.

At present, it takes technicians a few days to incubate and determine the existence of bacteria. But a new sensor does the work in just minutes. The sensor, which employs liposomes, has been able to rapidly detect traces of E. coli and other foodborne pathogens. For years, researchers have worked on improving methods for the rapid detection of pathogens. Currently it takes a few days to examine E. coli because the bacteria has to be cultured to obtain amounts sufficient for testing. The basis for the new sensor, liposomes, can contain fluorescent and visible dyes or other detectable compounds. Researchers can affix antibodies on the outside of liposome membranes. When a pathogen is detected, it binds to the antibodies, and the liposome membrane is ruptured, releasing the dye or other marker. In one format, paper-like test strips impregnated with liposomes were placed in a solution containing E. coli. As the liquid was drawn up the strip, it crossed the liposome-coated area. The pathogens were drawn to the antibodies on the liposome membrane, causing the membrane to react and rupture, releasing marker dye molecules. The change in color of the test strip indicated the presence of E. coli. Because each liposome contains perhaps millions of marker molecules, there is a large amplification effect when the liposome is ruptured and the markers are released. Since detection and signal amplification using liposome labels are not dependent on a secondary reaction--such as what is required for conventional enzyme-based tests--the liposomes provide an immediate indication of the pathogen. Contact: Richard Durst, Department of Food Science and Technology, Cornell University, Geneva, NY 14456. Phone: [phone]. Fax: [phone]. URL: www.cornell.edu.