I have an issue with SEM imaging of liposomes. When measured by DLS, they appear to be around 120 nm, but when using SEM with simple air drying, they appear much larger, around one micrometer.
Do you let them dry at room temperature, or do you use compressed air? Either way, when a droplet of water dries, it evaporates from the edges inward. During this process, the receding edge of the droplet pulls all the liposomes in the same direction, causing them to coalesce and form clumps and aggregates.
Therefore, samples for SEM should not be simply air-dried. They should first be fixed, for example, using malachite green, then completely dehydrated using a series of increasing ethanol concentrations, and finally bound to the base with glutaraldehyde. Otherwise there is no point of imaging with SEM, because it gives you no information about anything at all.
Aya Jab
Liposomes are formed by hydrophobic interactions mediated by water. The change in the state of water is responsible for the association of molecules. Therefore, neither DLS nor SEM are the methods that describe the true picture of the association of molecules in liposomes. For this, it is better to use small-angle X-ray scattering or cryo- TEM.
Cryo-EM is the accepted technique for imaging liposomes. They’re literally bags of fluid and air drying will cause irreversible damage with aggregation and agglomeration. There’s an ASTM standard for cryo-EM of liposomes.
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