See the Unseeable

When I was a graduate student in the 1970s, conventional wisdom held that light microscopy couldn’t resolve anything smaller than the wavelength of visible light (hundreds of nanometers). Electron microscopes overcame this size limitation but required “fixed” samples so no motions could be seen.

The dilemma this produces is that if you want to observe molecules, even relatively large ones like carbon nanotubes, you can’t also watch how they move in real time.

The stirrings of a solution to this problem come from the laboratory of Ahmed Zewail. Members of his Caltech research group conjured a new technique that essentially combines light and electron microscopy. Christened photon-induced near-field electron microscopy (PINEM), simultaneous impingement of femtosecond-long electron packets with intense optical pulses produces striking time-resolved images of carbon nanotubes and silver nanowires.

Although not applicable at this stage to aqueous biological systems like proteins and nucleic acids, PINEM is still an imaginative advance in molecular imaging, and it will be enormously useful to anyone interested in visualizing the world of nanostructures.

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