Transmission electron microscopy fixative preparation

Ultrastructural Analysis. Samples to be examined by electron microscopy were prepared as described by Persi and Burnham (19). All samples were fixed using the following schedule glutaral-dehyde (4% (w/v), 6h), osmium tetroxlde (20% (w/v), 6h) tannic acid (10% (w/v), 3h), and osmium tetroxlde (20% (w/v), 2h). Each fixative was prepared In 0.2M cacodylate buffer, pH 7.2, and samples were washed between fixations with cacodylate buffer. Subsequently, all cells were treated with uranyl acetate, washed, dehydrated through a graded ethanol series, and finally embedded In Maraglas (Polysciences, Inc.). Ultrathln sections were cut, post-stained with lead citrate and examined in a Phillips 300 transmission electron microscope operating at 60 Kv. 

Transmission electron microscopy (TEM) This technique is used when the MPCM is in nanometer size range. The specimen must have a low density, allowing the electrons to travel through the sample. There are different ways to prepare the material it can be cut in very thin slices either by fixing it in plastic or working with it as frozen material. Pan et al. studied nanostructures that were prepared through the methodology in-situ interfacial polycondensation. 

Transmission electron microscopy (TEM) is important to monitor cell-free sperm decondensation and nuclear formation. To prepare specimens for TEM, incubation mixture aliquots were fixed for 45 min in 2.5% (v/v) paraformaldehyde, 3.1% (v/v) glutaraldehyde, 0.02% (w/v) picric acid in 30 mAf NaHP04, pH 7.5. After fixation, samples were embedded in 2% (w/v) low-gelling-temperature agarose and postfixed for 15 min in 1% (w/v) OSO4. Samples may be dehydrated either in ethanol and propylene oxide or acetone and embedded for sectioning in Spurr s low-viscosity epoxy resin (Spurr, 1%9). Before examination, sections of about 70-nm thickness should be stained, e.g., with uranyl acetate and Reynolds lead citrate (Re)molds, 1%3). 

The interaction of MNPs with DNA is a well-known phenomenon [86-89], and single- or double-strand DNA is decorated by MNPs, which can easily be imaged by transmission electron microscopy (TEM) or AFM [90-92]. Various surface-functionalized AuNPs have been prepared to attach AuNPs securely to DNA molecules. In numerous studies, such AuNPs were prepared by surface modifications with cationic thiols [54, 55, 92] or intercalators [93, 94]. The ID chains of AuNPs coated with cationic trimethyl(mercaptoundecyl) ammonium monolayers were electrostatically assembled along DNA molecules in solution by the relative molar quantities of AuNPs and DNA base pairs. Since psoralen acts as a specific intercalator for A-T base pairs, the functionalized AuNPs were assembled onto the pA-pT ds-DNA [93]. Furthermore, UV irradiations induced the reaction between the psoralen units and the thymine of DNA, and then covalently fixed AuNPs to the DNA. 

A titania-coated silica, as prepared and calcined, was used as support to prepare two An catalysts. The catalysts were characterized by several techniques. X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), and tested in the CO Preferential Oxidation (CO PROX) reaction. The dispersion of Ti onto the silica was veiy homogeneous. On the other hand, the incorporation of Au was limited to less than 1 % and the particles size varied in the range 3-10 ran in both samples. Reaction studies were carri out on a fix bed reactor and on a Temporal Analysis of Products (TAP) reactor. The results reveal the participation of the surface -OH groups on the mechanism of the selective CO oxidation. 

Electron microscopy samples were prepared by techniques similar to that of Kato (8). Film samples were fixed with OSO4, potted in polymethyl methacrylate and then microtomed into thin sections ( 100 nm) for transmission examination using a Philips 100B electron microscope. 

Electron microscopy represents the only direct method that permits to see with our own eyes the interior of a sample with a resolution of a few nanometers. To characterize the texture of hypercrosslinked polystyrenes both transmission and scanning electron microscopy have been appfied. In the former case, ultrathin sections with a thickness of about 600 A were cut firom a sample fixed in epoxy resin, and then directly examined in transmission mode. Alternatively, two-step replicas have been prepared firom the cleavage face. To prepare the repfica the surface was first coated with a collodion film appfied from amyl acetate solution, and then with a carbon—platinum film. Finally, the collodion support was dissolved and the free carbon—platinum repfica examined under a transmission microscope. 

---