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ANAHEIM, Calif.--Like many objects of curiosity in the nanoworld, the DNA molecule has defied visual scrutiny because it lies beyond the "diffraction limit"--a 200 nanometer cutoff where the too-tiny escapes resolution by an optical microscope.
Dehong Hu and Peter Lu, scientists at the Department of Energy's Pacific Northwest National Laboratory in Richland, Wash., report today here at the American Chemical Society's national meeting that they have found their away around this barrier, combining FLIM, or fluorescence lifetime imaging microscopy, with AFM, atomic force microscopy.
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A blurry, pixilated FLIM image shows a cluster of florescence-tagged DNA molecules about one micrometer long. When FLIM is combined with an AFM technique that employs a gold-tipped silicon wand that can probe a sample without harming it, the molecule's structure is revealed.
The gold tip, Hu explains, generates a strong electrical field when illuminated by a laser; the electric field's interaction with the fluorescing molecules in the sample provides the image with its contrast.
Hu and Lu have also produced sharp images of fluorescing nanobeads, 40 nanometers diameter.
PNNL is a DOE Office of Science laboratory that solves complex problems in energy, national security, the environment and life sciences by advancing the understanding of physics, chemistry, biology and computation. PNNL employs 3,800, has a $600 million annual budget, and has been managed by Ohio-based Battelle since the lab's inception in 1965.