High-resolution biomolecule imaging


Rebecca Pool

Thursday, February 16, 2017 - 16:15
Image: Novel sensing method to produce high-resolution images of single biomolecules. [Nathan Fiske]
US-based researchers have developed a quantum sensor-based method for producing high-resolution images of individual biomolecules without requiring crystallization.
Based on 'quantum interpolation', the technique would even allow users to image specific sites within the molecules.
As lead researcher, Professor Paola Cappellaro from Nuclear Science and Engineering at MIT highlights, quantum sensors based on diamond crystals with nitrogen vacancy centres are used.
These vacancy centres render the crystals extremely sensitive to changes in magnetic and electric fields; when a molecule is close to the crystal, nitrogen vacancies near the crystal surface will respond to the nuclear spins within that molecule, and this response can be detected.
But while such sensors pave the way to high-resolution magnetic resonance imaging, progress has been thwarted by the frequency resolution of the sensor set-up.
"Nanoscale magnetic resonance imaging enabled by quantum sensors is a promising path toward determining the structure of single biomolecules at room temperature," says Cappellaro. "However hardware restrictions have limited sensor performance... with, for instance, finite sampling times [of the microwave pulses used to probe samples] limiting the achievable sensitivity and spectral resolution."
Given this, the researchers developed a technique called "quantum interpolation," which they claim improves the resolving power of such systems by more than a hundredfold.
According to Cappellaro, the method relies on quantum interference to achieve high-fidelity interpolation of the quantum dynamics between the time samplings allowed by the sensor hardware.
As she points out: "We try to mimic what the human eye does automatically, which is to move constantly and build up detail through multiple images of the same area, which the brain knits together into a single picture."
During image acquisition, the researchers optimise an applied microwave pulse sequence to achieve the resolution necessary to glean detailed structural information on the spin-state of individual atoms.
This data can then be used to help unravel the complex shapes of some biologically important proteins and other molecules, as well as other kinds of materials.
So far, the team's proof-of-principle experiments produced images of just the nuclear spin associated with the nitrogen vacancy centre within the diamond crystal, and the method will now be applied to actual biomolecules.
"All the various pieces [for molecular imaging] have been demonstrated.... and we will see if we can measure a single protein in its natural environment," concludes Cappellaro.
Research is published in PNAS.
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