Freezing, methods vitrification

There are four basic ways of freezing tissue or cells (Fig. 4.1). The most rapid freezing, vitrification, which holds each water molecule in place without the presents of ice crystals (Fig. 4.1, pathway No. 1). This method is difficult to perform and involves slamming the tissue onto a silver block at liquid helium (-214 C) temperature. For light microscopic immunocytochemistry, this method is not practical. 

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. 

Another solution-based method for material synthesis is based on the freezedrying of frozen aqueous solutions of components, followed by thermal decomposition of freeze-dried precursors [10]. The nitrates of a number of cations that are readily available and easily soluble in water are also used in this method. However, freezing of the nitrate solutions of transition metals and rare earth elements or their soluble complex compounds is accompanied by their vitrification [12]. Freeze-... 

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