ID-12-P-5925 In-situ TEM observation of crystal precipitation in liposomes filled with sodium chloride aqueous solution

Observation of chemical reactions using transmission electron microscope (TEM) reveals the details of the reaction, such as reactive sites and/or elementary process of the reaction. For instance, J. M. Yuk et al. had succeeded in in-situ observation of coalescence of two platinum nanocrystals in liquid encapsulated in graphene cells [1]. However, the graphene cells may not always suit for aqueous solutions since graphene is hydrophobic. Thus, another cell for aqueous solution is demanded and a liposome, which is composed of dipalmitoylphosphatidylcholine (DPPC) bilayers, is one of such cells. In this study, the precipitation process in liposomes filled with aqueous solution is observed using TEM.

The liposomes were synthesized using Bangham method [2]. In brief, DPPC layer reinforced with cholesterol were fabricated and the ultrasonication was conducted in sodium chloride aqueous solution to form the liposomes filled with the aqueous solution.

The prepared liposomes were directly observed without staining using conventional TEM (JEM-2000FX, JEOL) operated at 200 kV. TEM image of the synthesized liposomes is shown in Figure 1 and it is confirmed that the liposomes are successfully fabricated. Figure 2 is a continuous observation of the liposome. After electron irradiation, fluctuation on the contrast of the liposome takes place as shown in (a) and (b). In the final state (Fig. 2(c)), the precipitation of square nanocrystals is observed. According to the selected area electron diffraction pattern, the precipitated nanocrystals are sodium chloride single crystal. Thus, the chemical reactions in aqueous solution can be observed using liposome cells filled with water and solute.

[1] J.M. Yuk, et al. Science 336 (2012) 61.

[2] A.D. Bangham et al. J. Mol. Biol. 13 (1965) 238.