Dark field imaging optical microscopy

Transmission electron microscopy (TEM) resembles optical microscopy, except that electromagnetic instead of optical lenses are used to focus an electron beam on the sample. Two modes are available in TEM, a bright-freld mode where the intensity of the transmitted beam provides a two-dimensional image of the density or thickness of the sample, and a dark-field mode where the electron diffraction pattern is recorded. A combination of topographic and crystallographic information, including particle size distributions, can be obtained in this way [32],... 

Optical Contrast for Two-Dimensional Imaging Dark-Field Microscopy... 

Fig. 18.5 (a) Dark-field microscopy images of silver nanoparticles trapped in a microfluidic channel. The trapping wavelength was 830 nm. (b) Corresponding SERS spectra from the optically induced nanoparticle aggregates. A separate laser line at 514.5 nm was used to excite the Raman probes... 

However, finding out the position of an object with arbitrary precision is not the same as resolution, which is about separating similar objects at small distances. Localization per se cannot provide superresolution. This is also why, although it had been known and used for decades [109,110] and even routinely applied to single molecules [125,126], localization alone has not provided nanoscale images. (Note that in spite the use of localization in the 1980 s and earlier, near-field optical microscopy still seemed to be the only way to attain nanoscale resolution up to the early 1990 s.) Resolution clearly requires a criterion to discern objects or molecules, the simplest of which is bright vs. dark. ... 

Bright-Field Illumination A kind of illumination for microscopy in which the illumination of a specimen is arranged so that transmitted light remains in the optical path of the microscope and is used to form the magnified image. This is different from the arrangement in Dark-Field Illumination. 

Fig. 5.18 Dark-field optical microscopy images of long metallic nanoarrays prepared with a DNA nanofibers as template, (a) Large-area image of metallic nanoarrays, (b) Enlarged image with 40x objective, (c) Enlarged image with lOOx objective. The drying front moved from right to left. Reprinted with permission from [109]. Copyright (2010) by the Japan Society for Anedytical Chemistry...

Fig. 5.19 Dark-field optical microscopy images of Phenaz-TMA/AuNPs (a) before attaching DNA and (b) after attaching DNA. (c) Scattering spectra of spots 1, 2,3 and 4 in both images, (d) Schematic diagram of plasmon resonance energy induced by near-field coupling between MNPs...

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