Detector 1

FIGURE 16.6 Schematic diagram of a typical near-field scanning optical microscope (NSOM). The NSOM probe is a tapered optical fiber. Laser light is coupled into the fiber and is used to excite fluorophores as the probe scans across the sample surface. The probe-sample distance is maintained constant at <10 nm during scanning by shear-force-based distance detection in combination with an electronic feedback system controlling the piezoelectric scan stage. Fluorescence is collected by a conventional inverted microscope. Dual-channel optical detection allows wavelength and polarization discrimination. (From de Lange, F. et al., J. Cell Sci., 114, 4153, 2001.)

compared to far-field microscopy. In addition, the typical transmission efficiency through a pulled fiber is very low (~ 10~5—10~6 ). In addition, it is not possible to image molecules far from the sample surface as the near-field regime rapidly disappears with distance, preventing the use of NSOM to probe the interior of a cell. As a potential solution to some of these issues, apertureless NSOM probes have been proposed [73-75] in which an ultrasharp tip is used as an antenna to localize the excitation region.

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