Different approaches have improved the sensitivity of either electron or nuclear magnetic resonance to the single spin level. For optical detection it has essentially become routine to observe a single electron spin or nuclear spin.
Nuclear Magnetic Resonance Spectroscopy on a (5-nm)³ Sample Volume
Science 339, 561 (2013)
A new diamond based sensor is small and sensitive enough to probe the nuclear magnetic resonance (NMR) signal of a nanoscale sample volume. NMR is an interesting effect, in which information about a sample’s structure can be extracted by detecting the weak magnetic fields of certain atomic nuclei, such as hydrogen. It is well known for its application in clinical Magnetic Resonance Imaging (MRI), and is widely used in experimental science as well, but extensions to nanoscale samples have remained an elusive goal due to the insensitivity of conventional detection methods. The new diamond sensor overcomes these restrictions and paves the way towards “nanoMRI”.
NMR and MRI measurements on the nanoscale have been done so far only using magnetic force resonance microscopy (MRFM), a challenging experimental technique operating at low temperature in vacuum. The new approach utilizes a near-surface single nitrogen-vacancy (NV) center in diamond as a novel atomic size magnetic field sensor and functions even under ambient conditions.
The NV center gives the diamond a red fluorescent glow, which can be bright or dull depending on which way the NV’s electrons are spinning. Varying liquid and plastic samples were placed on the diamond surface and the weak magnetic field of the samples hydrogen spins interacts with the electrons of the NV center. The magnetic field of the hydrogen nuclei was detected by coherently manipulate the NV and looking onto its fluorescence. The sensor performance reaches voxel sizes down to (5nm) 3.
An important extension of this result will be the combination with a scanning probe setup, to implement NMR imaging on the nanoscale, potentially enabling the structural analysis of single molecules.
a) visiualization of the experimental setup – a single shallow NV center (red spot) allows for the detection of the weak magnetic field of hydrogen nuclei in a nanoscale sample volume (colored drop, upper figure half). b) NMR spectrum of the detected nuclei in the vicinity of the NV center. A strong contribution from the intrinsic 13 C inside the diamond (yellow) is accompanied by a weaker component of the 1 H nuclei of the sample (blue). Both components shift with the magnetic field at the gyromagnetic ratios of the respective spin species.
Nuclear Magnetic Resonance Spectroscopy on a (5-Nanometer) 3 Sample Volume
Staudacher, T., Shi, F., Pezzagna, S., Meijer, J., Du, J., Meriles, C. A., Reinhard, F. & Wrachtrup, J. Science 339, 561 (2013)