Interpreting turbidity measurements for vesicle studies

Spectrophotometers are routinely used to assess the turbidity of vesicle solutions. Here we provide guidelines for interpreting turbidity measurements of vesicle samples, and highlight potential pitfalls of the approach. We use an exact solution for core-shell scatterers to model and calculate how samples of vesicles scatter light, and provide a comprehensive overview of how the turbidity of vesicle samples can change with vesicle size, contents, and composition. Surprisingly, we find that vesicle lamellarity has a large effect on sample turbidity, while unilamellar vesicles of different sizes have similar turbidity. We use our model in conjunction with experimental data to measure the thickness of oleic acid vesicle membranes and find excellent agreement with values determined by cryo-TEM. We also calculate the effects of potential errors in measurement from forward scattering and multiple scattering.