Nanoscale NMR Spectroscopy and Imaging of Multiple Nuclear Species (1406.3365v1)

Abstract: Nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) are well-established techniques that provide valuable information in a diverse set of disciplines but are currently limited to macroscopic sample volumes. Here we demonstrate nanoscale NMR spectroscopy and imaging under ambient conditions of samples containing multiple nuclear species, using nitrogen-vacancy (NV) colour centres in diamond as sensors. With single, shallow NV centres in a diamond chip and samples placed on the diamond surface, we perform NMR spectroscopy and one-dimensional MRI on few-nanometre-sized samples containing $^1$H and $^{19}$F nuclei. Alternatively, we employ a high-density NV layer near the surface of a diamond chip to demonstrate wide-field optical NMR spectroscopy of nanoscale samples containing $^1$H, $^{19}$F, and $^{31}$P nuclei, as well as multi-species two-dimensional optical MRI with sub-micron resolution. For all diamond samples exposed to air, we identify a ubiquitous $^1$H NMR signal, consistent with a $\sim 1$ nm layer of adsorbed hydrocarbons or water on the diamond surface and below any sample placed on the diamond. This work lays the foundation for nanoscale NMR and MRI applications such as studies of single proteins and functional biological imaging with subcellular resolution, as well as characterization of thin films with sub-nanometre resolution.

• The paper demonstrates that NV centers in diamond can perform NMR spectroscopy with sensitivity sufficient to detect as few as 100 polarized nuclei.
• It employs both single and ensemble NV sensor modalities to achieve one-dimensional NMR and two-dimensional MRI with sub-micron spatial resolution.
• The study paves the way for applications in protein analysis, surface catalysis, and thin-film characterization by enabling nanoscale imaging under ambient conditions.

Nanoscale NMR Spectroscopy and Imaging Using NV Centers in Diamond

The paper under consideration presents an important advancement in the field of nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI), focusing on achieving nanoscale resolution by leveraging nitrogen-vacancy (NV) centers in diamond. Traditional NMR and MRI, while offering significant insights across various scientific fields, are constrained to macroscopic resolutions. This research endeavors to transcend these limitations by enabling nanoscale spectroscopic and imaging techniques under ambient conditions for multiple nuclear species, thus making it relevant for both fundamental and applied sciences.

Methodology and Results

The authors employ NV centers as quantum sensors capable of detecting minute magnetic fields generated by nuclear spins at the nanoscale. Their approach utilizes two primary sensor modalities:

1. Single NV Sensor: This modality uses shallow, single NV centers within a diamond chip to achieve high-resolution NMR spectroscopy and one-dimensional MRI on samples as small as a few nanometres. The paper demonstrated the ability to perform multi-species NMR on $^1$H and $^{19}$F nuclei with a statistical polarization equivalent to approximately 100 polarized nuclei.
2. NV Ensemble Sensor: In contrast, this modality implements a high-density layer of NV centers near the diamond surface to conduct wide-field optical NMR spectroscopy and two-dimensional MRI. It enables the interrogation of samples containing $^1$H, $^{19}$F, and $^{31}$P nuclei with sub-micron spatial resolution.

The experimental results assert the efficacy of this technology by demonstrating clear, species-specific NMR spectra for both sensor modalities. Notably, the paper identifies a ubiquitous $^1$H signal attributed to a $\sim$1 nm layer of adsorbed hydrocarbons or water on the diamond surface. These measurements not only substantiate the sensor's sensitivity but also highlight its capability to provide invaluable structural and compositional information at the nanoscale level.

Implications and Future Directions

This work lays the groundwork for potential applications in diverse scientific areas. The ability to perform NMR at the nanoscale opens avenues for the paper of single proteins, surface catalysis, and the imaging of biological cells with unprecedented cellular and subcellular resolution. Moreover, these findings suggest practical applications in materials science, where thin-film characterization with sub-nanometer precision is pivotal.

From a theoretical standpoint, the paper underscores the quantum mechanical principles that facilitate such high-resolution measurements. It accentuates the utility of NV centers in diamond as both robust and ambient-condition-operating sensors with promising scalability for large-scale imaging applications.

Looking ahead, research efforts could focus on enhancing the sensitivity and resolution of these NV-based sensors further, potentially by integrating very shallow NV centers with improved optical and spin properties. Additionally, deploying Fourier k-space imaging methods using pulsed magnetic field gradients could enhance the spatial resolution, pushing the boundaries of what is currently possible in nanoscale imaging.

In conclusion, the paper provides a compelling demonstration of NV-diamond NMR and MRI techniques, pioneering a path towards novel applications in scientific research at the nanoscale. The paper's contributions, both practically and theoretically, will undoubtedly influence future developments in quantum sensing and imaging technologies.