Researchers at IBM’s Almaden Research Center in San Jose, California, have detected the first faint magnetic signal from a single unpaired electron, paving the way for future efforts to produce three-dimensional images of molecules.
To make out the barely perceptible force, nanotechnologist Daniel Rugar and his team built a silicon cantilever one-thousandth the width of a human hair, attached a magnetic particle at the tip, and placed it near a so-called unpaired electron. By manipulating magnetic and electromagnetic fields, they flipped the electron’s orientation, changing the vibration frequency of the cantilever. Traditional magnetic resonance imaging works in a similar way, tracking the magnetic response of protons to assemble a 3-D image. However, Rugar says, “the magnetism from protons is very, very weak—you would need a million trillion protons in your sample just to pick up enough magnetic energy to make one pixel in the image.”
Pinpointing an electron via magnetic resonance is only the beginning of Rugar’s efforts to take 3-D pictures of biological molecules. Unpaired electrons are rare; most molecules are rich in protons, however. Since protons emit a magnetic force a fraction of the force of unpaired electrons, the team will have to improve the sensitivity of the cantilever, but Rugar is optimistic: “If we can make our magnetic tips smaller and place them closer to the sample, we should be able to improve the force we pick up by quite a large factor.”