An electron microscope that won't destroy living cells
By Darren Quick
October 6, 2009
We’ve all seen those scary images of monstrous looking insects captured by high-resolution electron microscopes, like the house dust mite in the image above. One thing you may not be aware of though, is that all the creepy crawlies in such images are dead. That’s because the particle beam of electrons used to illuminate a specimen also destroys the samples, meaning that electron microscopes can’t be used to image living cells. Electrical engineers at Massachusetts Institute of Technology (MIT) have proposed a new scheme that can overcome this critical limitation by using a quantum mechanical measurement technique that allows electrons to sense objects remotely without ever hitting the imaged objects, thus avoiding damage.
Traditional electron microscopes use a particle beam of electrons, instead of light, to image specimens, which offers extremely high resolution – up to 0.2 to 10 nanometers – that's 10 to 10,000 times greater than a traditional microscope. With the new quantum microscope proposed by the MIT researchers, the electrons would not directly strike the object being imaged, but would instead flow around one or two rings, arranged one above the other.
These rings would be close enough together that the electron could hop 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 Mehmet Fatih Yanik, senior author of the paper, says he expects the work "will likely ignite experimental efforts around the world for its realization, with perhaps the first prototype appearing in five years or so."
Before then technical challenges will need to be overcome, such as preventing the charged electron from interacting with other metals in the microscope. But Yanik believes that eventually such a microscope could achieve single-nanometer resolution, which would allow scientists to view molecules such as enzymes and nucleic acids inside living cells.
A non-invasive electron microscope could shed light on fundamental questions about life and matter, allowing researchers to observe molecules inside a living cell without disturbing them. If successful, such microscopes would surmount what Nobel laureate Dennis Gabor concluded in 1956 was the fundamental limitation of electron microscopy: "The destruction of the object by the exploring agent."
The MIT team’s research is detailed in the paper, "Non-destructive Electron Microscopy and Interaction-free Quantum Measurements,” which appears in the October issue of the journal Physical Review A – Rapid Communications.