Near-field optical microscopy using an organic thin films as a detection system and its application for the observation of biological specimens

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The near-field scanning optical microscope (NSOM) has been extensively investigated by many researchers, because it is possible with such a microscope to overcome the limitations of optical microscope resolution that are determined by the diffraction limit of light. The NSOMs can observe the refractive index in specimens. This is a unique advantage of NSOMs in comparison with other scanning probe microscopes such as the atomic force microscope (AFM) or the scanning tunneling microscope, which are very powerful tools in the measurement of specimen topography.Since the NSOMs require the scanning time of a probe tip to acquire an image of a specimen, they are difficult to apply to the observation of living specimens or moving biological specimens or very fast phenomena.We have developed a new type near-field microscope using an organic thin film as a detection system of light. In the near-field microscope, the optical field distributions near the specimens are recorded as the surface topography of a photosensitive film, and the topographical distributions are readout with an atomic-force microscope. Since the near-field microscope does not require the scanning of a probe tip for illumination or detection or scattering of light, it is possible to observe moving biological specimens and fast phenomena. We demonstrated the observation of a moving paramecium and euglena gracilis with subwavelength resolution.