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How Do I Determine The Size Of My Liposomes?

There are several techniques suitable for determining the size of liposome preparations. The most straight forward is analysis by quasi-elastic or dynamic light scattering. This provides the mean diameter and distribution of the particles. It can also distinguish whether the particle population is uniformly distributed around one or more particle sizes (unimodal vs. bimodal). Particle size can also be determined by electron microscopy. This technique does not allow for good characterization of the distribution of particle sizes and may suffer from changes to particle size induced by sample fixation and staining. Finally, size can be determined by measuring the volume of trapped internal contents using a fluorescent probe. In this technique a fluorophore is trapped in the internal compartment of the liposome and the liposome separated from non-trapped fluorophore. The trapped fluorphore is released and concentration measured. This information is used to calculate the internal volume of the liposome and thus the size particle that matches that volume. This technique assumes the liposome is unilamellar and therefore is not suitable for multilamellar liposomes.