Enhanced firefly bioluminescent assay of adenosine 5'-triphosphate using liposomes containing cationic cholesterols

Cationic liposomes composed of phosphatidylcholine and cationic cholesterols were prepared by extrusion technique. Dimethylaminoethyl-carbamoyl cholesterol (DMAE-chol) and diethylaminoethyl-carbamoyl cholesterol (DEAE-chol) were synthesized as a cationic cholesterol. Cationic liposomes containing DMAE-chol and DEAE-chol enhanced the intensity of maximum light emission from the firefly bioluminescent (BL) reaction. The sensitivity for ATP in the presence of cationic liposomes containing DMAE-chol and DEAE-chol was improved by a factor of 10 times compared to that in water alone. The detection limit for ATP upon using cationic liposomes was 1.0 pmol/L in an aqueous standard solution. The BL enhancement in the presence of cationic liposomes could be explained in terms of BL emitters and electrostatic interaction between the liposomes surface and BL reactants.