Electron microscopy artifact interpretation

Transmission electron microscopy (TEM) can provide valuable information on particle size, shape, and structure, as well as on the presence of different types of colloidal structures within the dispersion. As a complication, however, all electron microscopic techniques applicable for solid lipid nanoparticles require more or less sophisticated specimen preparation procedures that may lead to artifacts. Considerable experience is often necessary to distinguish these artifacts from real structures and to decide whether the structures observed are representative of the sample. Moreover, most TEM techniques can give only a two-dimensional projection of the three-dimensional objects under investigation. Because it may be difficult to conclude the shape of the original object from electron micrographs, additional information derived from complementary characterization methods is often very helpful for the interpretation of electron microscopic data. 

Since the work reported by McCartney et al. (9), ultrathin sections of other, more heterogeneous components and mixtures of components of coals of different rank have been prepared and observed. Procedures for minimizing artifacts have been learned and followed, and experience in observation has led to avoiding obvious faults. These sections were often not as large and continuous as those of homogeneous vitrinites, but adequate areas were available for electron microscopy. Observations of these various components revealed ultrafine structures of different size and form. Some of the structures can be correlated with those deduced from other direct or indirect study techniques others are unfamiliar and novel, and suggested interpretations are tentative. 

Although electron microscopy is always interpreted with care and caution, because of the possibility of artifacts, a picture is always of value in developing models of self-assembly products. In self-assembly experiments it is important to stop the process of self-assembly so that direct visualization... 

To prove the formation of vesicles a number of indirect techniques can be used such as dynamic light scattering, the use of fluorescent probes and pulsed field gradient NMR self-diffusion measurements. Some more direct techniques such as freeze-fracture and negative staining electron microscopy are less biased by the interpretation of the scientist, but also these methods have their limitations. Cryo-electron microscopy, as introduced by Dubochet in the 80s, is the method of choice when it comes to visualization of small colloidal structures. Recent developments in the vitrification of specimens make it now possible to observe vesicles and other aggregated structures artifact free. 

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