Selective staining

Figures 7 and 8 show the original morphologies of the block copolymers observed by TEM selectively stained P4VP, P2VP, and polyisoprene (PIP) sequences...

Selective staining of polysaccharide in the cell is said to depend upon the oxidizing action of periodate on such chemical configurations as a, p glycols and a-hydroxyketones. Polyaldehydes generated by this selective oxidation react with sulfite-decolorized fuchsin. Polysaccharide areas in the cell are colored red by the stain. 

MTX interferes with the growth of cancer cells by inhibiting the metabolism of folic acid. Drug efficacy was evaluated in vitro by MTT assay, as described above, and by Trypan Blue exclusion. Trypan Blue is a non-vital dye excluded by viable cells, but selectively staining dead cells. According to Figure 13.7, higher suppression of cell... 

Duckett JG, Read DJ, The use of the fluorescent dye, 3, 3 -dihexyloxacarbocy-anine iodide, for selective staining of ascomycete fungi associated with liverwort rhizoids and ericoid mycorrhizal roots. New Phytol 118 259—272, 1991. 

Figure 6.2. A cross section of Lycopodium clavata (club moss) showing that different types of cells are selectively stained by specific coloured dyes (Safranin O and haematoxylin). (Courtesy of Jim Haseloff, http //www.plantsci.cam.ac.uk/ffaseloff)...

In general, it is almost impossible to incorporate selective stains into polymers in a high enough concentration to produce contrast enhancement in thin sections [2]. An exception is the use of osmium tetroxide to stain unsaturated rubbers. 

Transmission electron micrography has, remarkably, been successfully used to image micelles formed by block copolymers in dilute solutions. Price and coworkers used two preparation methods. In the first method (Price and Woods 1973), f reeze etching, a drop of solution was rapidly frozen by quenching in liquid nitrogen. Solvent was then allowed to evaporate from a freshly microtomed surface of the droplet. Finally, a replica was made of collapsed micelles raised proud from the frozen surface. In the second method (Booth et al. 1978), a drop of micellar solution was allowed to spread and evaporate on a carbon substrate, and 0s04 was used to selectively stain one of the blocks. 

Fig. 2.7 (a) TEM micrograph from an /ps = 0.40, Nn = 209 PS-P2VP diblock, annealed at 140 °C for 6h then quenched in liquid nitrogen. Iodine was used to selectively stain the PVP. (b) SANS pattern from the same phase after preshearing at 140 °C (Schulz et al. 1996). (c) Possible orientations of the lam phase with respect to the shear coordinates. 

Fig. 2.20 TEM images from a PS-PI diblock with = 0.39 and M = 3.2 X Kfgmol"1, selectively stained with 0s04, showing (a) three-fold and (b) four-fold projections of the bicontinuous laSd structure (Forster et al. 1994).

Fig. 2.35 Transition from folded lace to worm-like micelle morphology in an /PS = 0.81 I2S copolymer (Pochan et al. 1996a). (a) TEM image of folded-lace structure, following annealing of the sample at 120°C for 1 week (0s04 was used to selectively stain the PI) (b) randomly oriented worm structure after annealing at 125 °C for 20 days (c) Schematic of the transition from lamellae via folded-lace to worm-like micelles.

Fig. 5.2 Transmission electron micrographs of a PS-PE diblock (M = 101 kg mol 11 wt% PE) (a) cast at 65 °C and annealed at 140 °C for 3h (b) cast from toluene at 65 °C (Cohen et al. 1990). The sample is stained with Ru04, which selectively stains PS.

Ba[Pt(CN)4] is used in the production of fluorescent X-ray screens.94 Dichlorodihydroxy-diamine- and dichlorodinitratodiamine-platinum(IV) complexes show weak fungicidal activity, but there appears to be no likelihood of them actually being used to this end.95 Other applications of platinum complexes involve their use as anticancer agents, as selective stains in biology, in catalysis, in metallurgy and in photography, described in the relevant chapters of this volume. 

The electron micrographs of the various ERL-4221-CTBN systems were prepared with the osmium tetroxide technique (3). The castings were stained by reaction with osmium tetroxide vapors for 24 hours. Ultrathin specimens, approximately 1000 A thick, were cut with the Reichert OMU2, ultramicrotome equipped with a diamond knife and were stained again for one hour. The osmium tetroxide selectivity stained the rubber phase, while the epoxy remained unaffected, revealing many structural features in the polyphase systems with excellent contrast and... 

Contrast in the TEM increases as the atomic number of the atoms in the specimen increases. Since biological molecules are composed of atoms of very low atomic number (carbon, hydrogen, nitrogen, and so on), contrast is increased with a selective staining, obtained by exposure of the specimen to salts of heavy metals, such as uranium, lead, and osmium, which are electron opaque (www.hei.org/research/depts/aemi/emt.htm). 

---