Figure 1.

Assay schematic. (Top) Hydrolysis of the phosphate–oxygen bond of SM by SMase to produce ceramide and phosphocholine (not shown). (Bottom) Action of SMase on BSM:Chol liposomes encapsulating cysteine leads to a composition-driven membrane phase change with the formation of ceramide-rich gel domains and partitioning of cholesterol into remaining SM domains. This causes cysteine leakage and aggregation of subsequently added gold nanoparticles by formation of hydrogen bonds between cysteine molecules on adjacent nanoparticles. Graphic of SMase enzyme structure is adapted from Ago etal.³⁸