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Published June 1, 2010 | Published
Journal Article Open

Biological imaging with 4D ultrafast electron microscopy


Advances in the imaging of biological structures with transmission electron microscopy continue to reveal information at the nanometer length scale and below. The images obtained are static, i.e., time-averaged over seconds, and the weak contrast is usually enhanced through sophisticated specimen preparation techniques and/or improvements in electron optics and methodologies. Here we report the application of the technique of photon-induced near-field electron microscopy (PINEM) to imaging of biological specimens with femtosecond (fs) temporal resolution. In PINEM, the biological structure is exposed to single-electron packets and simultaneously irradiated with fs laser pulses that are coincident with the electron pulses in space and time. By electron energy-filtering those electrons that gained photon energies, the contrast is enhanced only at the surface of the structures involved. This method is demonstrated here in imaging of protein vesicles and whole cells of Escherichia coli, both are not absorbing the photon energy, and both are of low-Z contrast. It is also shown that the spatial location of contrast enhancement can be controlled via laser polarization, time resolution, and tomographic tilting. The high-magnification PINEM imaging provides the nanometer scale and the fs temporal resolution. The potential of applications is discussed and includes the study of antibodies and immunolabeling within the cell.

Additional Information

© 2010 by the National Academy of Sciences. Contributed by Ahmed H. Zewail, April 26, 2010 (sent for review April 17, 2010). Published online before print May 17, 2010. We thank Prof. M. R. Hoffmann for use of the sonicator. This work was supported by the National Science Foundation, the Air Force Office of Scientific Research, and the National Institutes of Health in the Center for Physical Biology supported by the Gordon and Betty Moore Foundation Caltech. Author contributions: D.J.F., B.B., and A.H.Z. designed research, performed research, contributed new reagents/analytic tools, analyzed data, and wrote the paper. The authors declare no conflict of interest.

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