Photon scanning tunneling microscopy of unstained mammalian cells and chromosomes

The photon scanning tunneling microscope (PSTM) yields topographical images of samples which are thin or which are transparent at the wavelength used. A wide range of samples sizes may be imaged extending to well below the diffraction limit, but samples on the order of several to many micrometers in size can be analyzed if total internal reflection occur in the sample. We have used the PSTM to examine the topography of mouse and human cells and of mouse chromosomes that are unstained. Our objectives were to compare the images as an improved resolution alternative to phase contrast microscopy, and to provide a sample preparation methodology that will permit localized simultaneous fluorescence or absorption spectroscopy with the signal collected by the probe tip of the PSTM. Further, the PSTM's ability to produce topographical profiles was tested in order to establish the basis for future investigation of possible structural abnormalities in the chromosomes. That is, we had both physical and biological objectives to consider. To this end we utilized the 442 nm line of a HeCd laser, the resulting image quality being tested partly on order to ascertain the increase effects of Rayleigh scattering relative to results at longer wavelengths. It is shown that adequate resolution and signal-to-noise ration can be obtained with the shorter wavelength even in the presence of intensity fluctuations from the laser, thus showing that fluorescence and absorption can be expected to be practicable.