A multi-functional liposome has been developed that demonstrates reversible changes in color and fluorescence intensity in response to changes in pH. Addition of a pendant tryptophan moiety gives the assembly the ability to detect Escherichia coli. The sensor platform is made from a polymerized vesicular assembly of hydrazide-terminated diacetylene lipids and a BO558 fluorescent dye. The polymer backbone is responsible for the color change, while the organization induced by hydrogen bonding of the terminal hydrazide groups permits the reversibility of the color change. Fluorescence quenching is due to internal rearrangement of the liposome and occurs in both polymerized and unpolymerized structures. (C) 2008 Elsevier Ltd. All rights reserved.