PHOTON SCANNING-TUNNELING-MICROSCOPY OF UNSTAINED MAMMALIAN-CELLS ANDCHROMOSOMES

The photon scanning-tunneling microscope (PSTM) yields optical topogra phical images of samples that are thin or that are transparent at the wavelength used. A range of sample sizes can be imaged extending to we ll below the diffraction Limit for sufficiently flat samples. But samp les of the order of several to many micrometers in size can be analyze d with less-refined resolution if total internal reflection can be mad e to occur in the sample. We used the PSTM to examine the optical topo graphy of mouse and human cells and of chromosomes that are unstained. Our objectives were to demonstrate the images as an alternative to co nventional microscopy and to provide a sample-preparation methodology that will later permit localized, simultaneous fluorescence or absorpt ion spectroscopy with the signals collected by the probe tip. Furtherm ore, the PSTM's ability to produce optical profiles in air and in wate r was tested to establish the basis for future investigation of possib le abnormalities in the chromosomes. That is, we considered both physi cal and biological objectives. To this end we utilized the 442-nm line of a He-Cd laser as well as the 633-nm line from a He-Ne laser, the r esulting image quality being tested partly to ascertain the increased effects of scattering at the smaller wavelength. It is shown that adeq uate resolution and signal-to-noise ratio can be obtained with the sho rter wavelength Even in the presence of intensity fluctuations from th e laser, thus showing that fluorescence and absorption studies can be expected to be practicable. (C) 1998 Optical Society of America OCIS c odes: 170.1530, 180.0180, 180.5810.