Researchers at the University of Stuttgart and Max Planck Institute for Solid State Research in Germany have made quite a breakthrough by being able to study the atom by atom molecular configuration of proteins using a miniaturized version of an MRI scanner. These days the structures of individual protein molecules are impossible to see and various methods, including computer simulations, are used to obtain the probable atomic configuration of protein structures.
The new method relies on a very small nuclear magnetic resonance sensor that was developed a few years ago but that was not precise enough to resolve atoms. The German team have since been doing a bit of physics and engineering thinking and tinkering, overcoming what many thought was impossible.
From Max Planck Society:
To achieve atomic-level resolution, the researchers must be able to distinguish between the frequency signals they receive from the individual atoms of a molecule – in the same way as a radio identifies a radio station by means of its characteristic frequency. The frequencies of the signals emitted by the atoms of a protein are those frequencies at which the atomic bar magnets in the protein spin. These frequencies are very close together, as if the transmission frequencies of radio stations all tried to squeeze themselves into a very narrow bandwidth. This is the first time the researchers in Stuttgart have achieved a frequency resolution at which they can distinguish individual types of atoms.
The sensor, which acts as a minute NMR antenna, is a diamond with a nitrogen atom embedded into its carbon lattice close to the surface of the crystal. The physicists call the site of the nitrogen atom the NV centre: N for nitrogen and V for vacancy, which refers to a missing electron in the diamond lattice directly adjacent to the nitrogen atom. Such an NV centre detects the nuclear spin of atoms located close to this NV centre.
The spin frequency of the magnetic moment of an atom which has just been measured is transferred to the magnetic moment in the NV centre, which can be seen with a special optical microscope as a change in colour.
The quantum sensor achieves such high sensitivity, as it can store frequency signals of an atom. One single measurement of the frequency of an atom would be too weak for the quantum sensor and possibly too noisy. The memory allows the sensor to store many frequency signals over a longer period of time, however, and thus tune itself very precisely to the oscillation frequency of an atom – in the same way as a high-quality short-wave receiver can clearly resolve radio channels which are very close to each other.
This technology has other advantages apart from its high resolution: it operates at room temperature and, unlike other high-sensitivity NMR methods used in biochemical research, it does not require a vacuum. Moreover, these other methods generally operate close to absolute zero – minus 273.16 degrees Celsius – necessitating complex cooling with helium.
Image: Green laser light transmitted via an optical fibre excites nitrogen atoms in a diamond, causing it to fluoresce with a red light. The brightness of a nitrogen atom at the edge of the diamond lattice allows conclusions to be drawn about the magnetic signals from a sample on the surface of the sensor. © University of Stuttgart
Study in Science: Nanoscale nuclear magnetic resonance with chemical resolution…
Via: Max Planck Society
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