Liposome-based sensor for the detection of bacteria

Identification and quantification of bacteria affecting human life, directly causing diseases and indirectlycontaminating natural ecosystems, are mostly carried out by expensive and time-consuming meth-ods. There is the need for rapid and economic ways for detecting bacteria in the environment andin clinics. We propose the use of engineered liposomes for detecting bacteria in drinking water. Ourapproach exploits cationic liposomes functionalized with a surface potential-sensitive fluorophore, 4-heptadecylumbelliferone (C17-HC). The interaction between liposomes and bacteria involves a changein the surface potential experienced by C17-HC and switches on an optical signal.We investigated, by DLS, zeta-potential and fluorescence experiments, a large number of cationic lipo-somes formulated with a natural phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), C17-HC, and one of three synthetic cationic compo-nents, differing from each other for the number of unsaturations on the polar ammonium head, two ofwhich ad hoc synthesized. Then we evaluated the ability of liposomes to produce a fluorescent signalupon interaction with three bacterial strains, Staphylococcus aureus, Escherichia coli and Enterococcus fae-calis; moreover, we analyzed the fluorescent response of each liposome formulation in the presence ofthe three bacterial strains at the same time, in order to simulate a real scenario. We found that interactionwith bacteria triggers an optical signal in six of the evaluated formulations, resulting responsive downto 102CFU/mL of bacteria suspended in pipeline water coming from the water main of Rome (Italy).