Liposomes are nowadays frequently used as drug delivery systems, and as such requires that they are well characterised for manufacturing and batch release. This characterisation includes their size and size distribution.
For these parameters, dynamic light scattering (DLS) is commonly used to characterise size and size distribution and also nanoparticle tracking analysis (NTA) has previously been shown to be useful for measuring liposomes size and concentration.
Multi-angle DLS (MADLS®) based particle concentration measurement in the Zetasizer Ultra is capable of measuring the particle concentration, as well as size and size distribution of a range of dilutions of a liposome sample. A comparison will be made with NTA measurements of the same samples.
Experimental method
The liposomes used were Formumax HSPC/CHOL liposomes, which were diluted using Gibco PBS at pH 7.2 using gravimetric dilution protocol.
A Zetasizer Ultra and NanoSight NS300 were used to measure the liposomes at 25°C. The samples were measured five times on the Zetasizer Ultra using the particle concentration measurement. Using the NanoSight NS300, five videos of 60 seconds each were recorded while using the syringe pump and a 405nm laser.
Nominal dilutions from stock concentration down to a 1:1,000,000 dilution were measured on the Zetasizer Ultra. The 1:10,000,000 dilution was not measured as there was not enough signal at side scatter detector for the instrument to be able to accurately measure the size and therefore the concentration.
The NanoSight NS300 was used to measure the dilutions from 1:10,000 to 1:10,000,000. Above 1:10,000 the samples were too concentrated for the NS300 instrument.
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