Polydiacetylene-Based Liposomes: An "Optical Tongue" for Bacteria Detection and Identification.

Food- and water-borne bacteria are a major health concern worldwide. Current detection methods are time-consuming and require sophisticated equipment that is not always readily available. However, new techniques based on nanotechnology are under development that will result in a new generation of sensors. In this experiment, liposomes are synthesized that consist of a bacteria-sensing structure on the outer surface and a polydiacetylene signal transducer. The sensor gives a dramatic blue-to-red color change in the presence of lipopolysaccarides (LPS) extracted from bacteria cell walls. The treatment of slightly different liposomes under multiple analysis conditions may be used to create a sensor array (an optical tongue) that is able to distinguish between LPS derived from different Gram-negative bacteria. The experiment introduces students to concepts of self-assembly, supramolecular synthesis, biosensor design, and to the basic structure of bacteria cell walls. It also readily lends itself to expansion as an investigative-learning experience through student-led modification of the liposome structure.