Analytical techniques for single-liposome characterization

Abstract

Liposomes or phospholipid vesicles are one of the most versatile nanoparticles used to convey drugs, vaccines, genes, enzymes, or other substances to target cells and as a model to mimic biological membranes. To fulfil their roles in drug delivery and biotechnology, the physical and chemical properties of liposomes, such as size, shape, chemical composition, lamellarity, encapsulation efficiency of cargo molecules, and the density of proteins reconstituted in the membrane, need to be characterized to ensure reproducible preparation of the vesicles. Compared to bulk analysis, techniques focusing on the individual analysis of liposomes can reveal heterogeneity that is otherwise masked by ensemble averaging. Herein, we review the recent advances in techniques for single-liposome characterization.

Selecting analytical tools for characterization of polymersomes in aqueous solution

“…There have also been extensive studies related to specific types of analysis such as EM 64,111 , fluorescence microscopy 112 , mechanical manipulation 79,80 , single particle techniques like NTA 37 , AFM 40,113 and scanning tunneling microscopy (STM) 70 . Comparative analysis reviews have been presented for liposomes 39,54 , whereas for some polymersome reviews, characterization methods generally only constitute a smaller part of the review, see 8,55 .…”

“…In the case of visualization methods, Small-angle x-ray and neutron scattering (SAXS and SANS) that were used in the study, the SDL is measured from own experiments. 49,63,64 Uncertainty in true size Transmission electron microscopy Cryo-TEM 0.1 Size, lamellarity, morphology Structure preservation Freezing artifacts 49,65 Uncertainty in bilayer thickness Scanning electron miscroscopy Freeze fracture Cryo-SEM 2 Size, lamellarity, morphology 3D appearance Freezing artifacts 66,67 Scanning electron microscopy Environmental SEM 30 Size, lamellarity, morphology, concentration Native environment Poor resolution 40,60,68 Electromagnetic manipulation methods Scanning probe microscopy 3D information High sensitivity to vibration Scanning probe microscopy Atomic force microscopy 1 Size, topology, elastic properties Sensitivity Shape alteration upon attachment 37,40,54,60,69 Scanning force microscopy Amphiphile adsorption on cantilever Scanning probe microscopy Scannig tunneling microscopy 0.1 Size, topology No mechanical contact to sample Cantilever tip condition crucial 70,71 Nuclear magnetic resonance P 31 -nuclear magnetic resonance Lamellarity High accuracy Signal decrease due to convenient buffer [72][73][74] Electron paramagnetic resonance Encapsulation, bilayer flexibility, 40,75,76 Electron spin resonance bilayer polarity, lamellarity Specific to unpaired electrons Signal decrease due to water Laser doppler electrophoresis Zeta potential, surface charge potential Fast Calibration required frequently 77,78 Optical 54,86 ever care has to be taken when interpreting polydisperse samples, which are the case with most polymers and most preparation methods. Small-angle X-ray 33 or neutron scattering (SAXS or SANS; resolution limit of both: 0.5 nm) 34 provide detailed information about the polymersome bilayer 35 , but due to the need for access to large scale radiation facilities, their use for routine measurem...…”

Development of a lipid-based delivery system for the chemotherapeutic compound SN-38

“…Liposomes are intrinsically highly heterogeneous assemblies, exhibiting different physical and chemical properties (e.g. size, lipid composition, encapsulation efficiency) even within a same batch [48]. Therefore, successful implementation of liposome-based drug delivery systems requires characterization of those properties at the single nanoparticle level.…”

“…Therefore, successful implementation of liposome-based drug delivery systems requires characterization of those properties at the single nanoparticle level. Transmission electron microscopy is a powerful technique to characterize the size, morphology and lamellarity of individual liposomes [48] and can be used as well for examining the heterogeneity of drug encapsulation yield in vesicles [49, 50]. However, this technique necessitates laborious sample preparation and allows the analysis of only a small fraction of the sample.…”

Nano based drug delivery

“…In order to determine the quality of liposomes and to obtain quantitative measures, the main characterization methods include observation of visual appearance and measurement, of size distribution, surface charge phospholipid content, lamellarity, composition, concentration of degradation products, encapsulation efficiency, and stability [195,215,[222][223][224].…”