Water-soluble organic nanoparticles were prepared by cross-linking the micelles of a tripropargylated cationic surfactant by a diazide cross-linker in the presence of Cu(I) catalysts. The nanoparticles were decorated with hydrophilic ligands of different lengths on the surface. By interacting with negatively charged liposomes through tunable electrostatic interactions, these nanoparticles induced fusion and leakage of large unilamellar vesicles (LUVs). Fusion or aggregation of the membranes was highly sensitive to the rigidity and phase structures of the membranes, enabling thermally gated fusion to occur within a very narrow window of temperature change.