Determination of liposome size distribution by flow cytometry

Background: An essential parameter that describes the quality of liposome s uspensions is the mean size, respectively the size distribution. Currently several analytical methods including laser light scattering techniques (LLS T) are being employed. Methods: Here we present an alternative technique using flow cytometry (FCM ) to characterize uni- and poly-disperse suspensions. As model liposomes pr eparations containing dipalmitoylphosphatidylcholine (DPPC) were used. A co nstant number of particles (1,500/s) in the fluid stream and a representati ve number of 10,000 particles of each sample was measured. Fluorescence-lab eled latex beads were measured identically, and their side scatter signals were calibrated and correlated to the results obtained with Liposome vesicl es. Results: Evaluation of the measurement and validation of the FCM results in comparison to LLST confirm the reliability of results obtained with our me thod. Latex beads in the range of 100-1000 nm were used for calibration to classify liposomes. Altough measurement characteristics and calculation in both methods are basically different, very good agreement of the results wa s achieved. Conclusions: Demonstration of stability, reproducibility, and reliability o f results make the employment of this method acceptable for an adequate rou tine analysis technique. Cytometry 39:166-171, 2000. (C) 2000 Wiley-Liss, I nc.