NM-RESOLUTION VISIBLE-LIGHT MICROSCOPY, of a sort, has been accomplished by scientists at the Max Planck Institute for Biophysical Chemistry in Gottingen, Germany (Stefan Hell, 011-49-551-201-1366, shell@gwdg.de). The diffraction of light waves normally limits spatial resolution of nearby objects to no better than the wavelength of the light source. So called near-field microscopy beats this limit by moving the source very close to the subject to be imaged. But the Gottingen group, whose work is an example of far-field microscopy, in this case does not so much beat the diffraction limit as circumvent it. They split a laser pulse (wavelength of 820 nm) into two parts and illuminate a sample consisting of beads attached to a Langmuir-Blodgett layer, the kind of filmlike layer of water-hating and water-attracting molecules poised back-to-back that forms the membrane of most cells. The sample, positioned close to the place where the two laser beams meet at the same focal point of two lenses, starts to fluoresce. This fluorescence is viewed through filters at two different colors.
This "confocal" microscopy does not exactly "resolve" the objects apart but does measure the distance between them with a precision as high as 1.2 nm. For the process to work, however, the contrasting objects, in this case the layer and a bead, must fluoresce at different colors. This is just what one gets when attempting the co-localization of proteins and organelles or vesicles and membranes, etc. And unlike such imaging techniques as atomic force microscopy (AFM) or transmission electron microscopy (TEM), the use of non-bleaching visible light permits the study of living cells. (Schmidt et al., Review of Scientific Instruments, July /pnu/2000/; Select Article.)
