Darkfield

Light microscopy allows, in comparison to other microscopic methods, quick, contact-free and non-destmctive access to the stmctures of materials, their surfaces and to dimensions and details of objects in the lateral size range down to about 0.2 pm. A variety of microscopes with different imaging and illumination systems has been constmcted and is conunercially available in order to satisfy special requirements. These include stereo, darkfield, polarization, phase contrast and fluorescence microscopes. 

Fig. 1. Darkfield illumination the image is formed by light scattered from the specimen detail against a dark field.

The contrast for specimen detail in the field of view is gready enhanced by darkfield illumination (10). The degree of contrast and sensitivity of detection of smaH-object details depend on the relative indices of the specimen and the mounting Hquid and on the intensity of the illumination. Darkfield illumination is not, however, a satisfactory solution for biologists who need direct transmitted light in order to observe specimens, especially stained specimens. It is, however, very usefiil in detecting asbestos fibrils that often exist in door tiles or water and air samples as 20-nm fibers (10 times finer than the resolution of an asbestos analyst s usual microscope) (11). Darkfield illumination yields an uimatural appearance and difficulties in interpretation hence, a need for better contrast methods stiU exists. 

The electron microscope is also used in the darkfield mode, in which it improves contrast between different chemical phases or different orientations of a given soHd phase. 

The schlieren microscope is able to detect refractive index variations to six decimal places. Any small difference in optical path (index difference, film thickness, etc) is very precisely detected by the schlieren microscope, especially in the Dodd modification. It is, in effect, a darkfield method. The specimen is illuminated with light in a portion of the illuminating cone and that direct light is masked in the conjugate back focal plane of the objective (Fig. 3). The only light to pass through this plane is refracted, reflected, or diffracted by the specimen. 

Darkfield microscopy is one of the oldest modes of microscopy. Here, axial rays from the condenser are prevented from entering the objective, through the use of an opaque stop placed in the condenser, while peripheral light illuminates the specimen. Thus, the specimen is seen lighted against a dark Held. 

But darkfield conventional transmission electron microscopy can now reveal monatomic steps directly, as the micrograph in Fig. 12 shows (71). Using this kind of approach it should be possible to ascertain quantitatively the extent of the interaction between a catalyst and its underlying support. 

Sexually transmitted diseases When treating gonococcal infections in which primary and secondary syphilis are suspected, perform proper diagnostic procedures, including darkfield examinations and monthly serological tests for at least 4 months. Resistance The number of strains of staphylococci resistant to penicillinase-resistant penicillins has been increasing widespread use of penicillinase-resistant penicillins may result in an increasing number of resistant staphylococcal strains. 

Monitoring In sexually transmitted diseases when coexistent syphilis is suspected, perform darkfield examination before starting treatment and repeat the blood serology monthly for at least 4 months. 

Syphilis In the treatment of sexually transmitted disease, if concomitant syphilis is suspected, perform a darkfield examination before treatment is started. Perform monthly serologic tests for 4 months or more. 

Fig. 46a d. Darkfield optical micrographs of tubules formed by addition of water to ethanol solutions of 21 (m = 8, n = 9). The micrographs were taken at room temperature. With little water the tubules were uniformly long - some in (d) are longer than 300 pm. The final concentration of the lipid was 0.5 mg/ml in all cases. The final concentrations (v/v) of ethanol were a 50% b 55% c, d 70%. The incubation times in the ethanol-water mixtures were 10 h (a, b), 144 h (c), and 6 months (d). Scale bars = 100 pm [361]... 

For optical microscopic examination, a Zeiss Axioplan microscope and brightfield (BF), darkfield (DF), polarized light (P) and differential interference... 

Darkfield (DF) imaging was performed with the tilted beam technique, the reflection selected by a 6 x 10 3 rad.objective aperture. 

Photoresist Preparation and Lithographic Processing (Darkfield Formulation)... 

Figure 4.4 Schematic of the experimental apparatus used for single-particle darkfield scattering spectroscopy.

Figure 4.5 (A) Darkfield optical micrograph of a typical distribution of single Ag nanoparticles immobilized on a glass cover slip. (B) Single-particle darkfield scattering spectra corresponding to the individual Ag nanoprisms labeled in (A). The ensemble solution extinction spectrum is shown as the shaded, dashed curve for comparison. Reprinted with permission from reference 9.

Figure 4.7 (A) Schematic illustration of fluorescence enhancement experiment Ag nanoprisms are adsorbed on top of monolayer of Rhodamine red on glass slide. (B) Darkfield scattering image of an area of the substrate. Each of colored...

Figure 4.8 Specific DNA-directed coupling of fluorescent dyes to Ag nanoprisms. (A) Darkfield optical micrograph showing a field of isolated Ag nanoprisms. (B) Incubation of the DNA-functionalized particle field in with non-complementary dye-labeled DNA results in little detectable fluorescence. (Q Subsequent hybridization of the same sample with complementary Rhodamine Red-labeled DNA leads to attachment of the dye and visible fluorescence from the functionalized nanoparticles. Reprinted from reference 9.

Figure 4.9 (A) Darkfield optical micrograph of four individual Ag nanoparticles that have been hybridized with a 1 1 mixture of the dyes Alexa Fluor 488 and Rhodamine Red. (B) Fluorescence micrograph of the same area collected using Alexa Fluor 488 excitation eind emission. (C) Fluorescence micrograph of the same area collected using Rhodamine Red excitation and emission. (D) Single particle scattering spectra show the LSPR for each particle in (A). Reprinted from reference 9.

Figure 4.5 (A) Darkfield optical micrograph of a typical distribution of single Ag nanoparticles immobilized on a glass cover slip. (See text for full caption.)...

Figure 2 Darkfield transmission electron micrographs, (a) Solar-wind sputtered rim on exterior surface plus implanted solar flare tracks in chondritic IDP U220A19 (from Bradley and Brownlee, 1986). (b) Solar flare tracks in a forsterite crystal in chondritic IDP U220B11 (from Bradley et al., 1984a). The track densities in both IDPs are...

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