Methods for measuring the size of the liposomes may vary in complexity. The most precise method for determining the size of the liposomes is electron microscopy. Each individual liposomes can be viewed by electron microscope and with enough patience, time and skills to avoid numerous artifacts, one can obtain very accurate information about the profile of a liposome population over the whole range of sizes. The main problem is that the technique can be very time consuming (at least 400 liposomes should be counted for each batch of liposome) In addition to that electron microscopes are quite expensive and can only be operated by a highly trained microscopist.
Laser light scattering analysis is fairly rapid and simple to perform, however it measures an averaged property of the bulk of the liposomes. Laser light scattering analysis will only provide useful information on the size distribution for liposomes up to 1 um. The size of the liposome particles that are larger than one micron can be determined by a Coulter counter that uses laser diffraction (e.g. Mastersizer) or uses obstruction techniques (e.g Accusizer).
In the next blog, the principle of liposome size measurement by photon correlation spectroscopy will be explained in detail.