Major Advance in Electron Microscopy

Electrical engineers have proposed a new strategy that can overcome a critical limitation of high-resolution electron microscopes: they cannot be used to image living cells because the electrons destroy the samples. The researchers suggest using a quantum mechanical measurement technique that allows electrons to sense objects remotely without ever hitting the imaged objects, thus avoiding damage.

A noninvasive electron microscope could provide clues into essential questions about life and matter, allowing researchers to observe molecules inside a living cell without disturbing them. If successful, such microscopes would overcome what Nobel laureate Dennis Gabor concluded in 1956 was the fundamental limitation of electron microscopy: "The destruction of the object by the exploring agent.”

Conventional electron microscopes utilize a particle beam of electrons, instead of light, to image specimens. These beams offer extremely high resolution, up to 0.2 nm – 10 nm, or 10 to 1,000 times greater than a traditional light microscope. In contrast, with the new proposed quantum mechanical setup, electrons would not directly strike the object being imaged. Instead, an electron would flow around one of two rings, arranged one above the other. The rings would be close enough together that the electron could jump easily between them. However, if an object (such as a cell) were placed between the rings, it would prevent the electron from hopping, and the electron would be trapped in one ring.

This setup would scan one pixel of the specimen at a time, putting them all together to create the full image. Whenever the electron is trapped, the system would know that there is a dark pixel in that spot.

Assistant professor Dr. Mehmet Fatih Yanik, from the Massachusetts Institute of Technology (MIT; Cambridge, MA, USA), and senior author of the article, published in the October 2009 issue of the journal Physical Review A, reported that he expects the project "will likely ignite experimental efforts around the world for its realization, with perhaps the first prototype appearing in five years or so.”

Although technical challenges need to be overcome (such as preventing the charged electron from interacting with other metals in the microscope), Dr. Yanik believes that eventually such a microscope could achieve single-nanometer resolution. That level of resolution would allow scientists to view molecules such as enzymes and nucleic acids inside living cells.

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Massachusetts Institute of Technology