Nitrogen-vacancy diamond magnetometry of biological cells in two papers

Short answer: Nitrogen-vacancy (NV) centres in diamond can act as optical magnetic field sensors, and two papers used them to map magnetic fields from living and fixed biological samples. A 2013 Nature paper imaged magnetotactic bacteria at 400 nanometre resolution, and a 2017 Nature Communications paper mapped fields in mammalian cells and tissues with submicron resolution and nanotesla sensitivity. Both are laboratory demonstrations.

Why image magnetic fields in cells?

The 2013 abstract sets out the gap. Magnetic imaging is a powerful tool for probing biological and physical systems, but the authors say existing techniques either have poor spatial resolution compared with optical microscopy, as with magnetic resonance imaging, or require conditions that rule out living samples while giving submicrometre resolution, as with scanning superconducting quantum interference device microscopy, electron holography and magnetic resonance force microscopy.

What did the 2013 experiment do?

The authors demonstrate magnetic imaging of living cells, specifically magnetotactic bacteria, under ambient laboratory conditions and with sub-cellular spatial resolution of 400 nanometres. The sensor is an optically detected magnetic field imaging array made from a nanometre-scale layer of nitrogen-vacancy centres implanted at the surface of a diamond chip. Bacteria are placed on the diamond surface, the NV quantum spin states are probed optically, and images of the vector components of the magnetic field created by chains of magnetic nanoparticles, called magnetosomes, are reconstructed rapidly. The magnetic maps were spatially correlated with optical images from the same apparatus. Wide-field microscopy allows parallel optical and magnetic imaging of multiple cells with submicrometre resolution and a field of view above 100 micrometres, and scanning electron microscope images of the bacteria confirm that the correlated images can locate and characterise the magnetosomes in each one.

What did the 2017 paper add?

The 2017 paper starts from magnetic resonance imaging, which the authors say gets much of its contrast from microscale magnetic field patterns in tissue. They say the link between those patterns and macroscale MR images had not been studied directly because there was no way to map microscopic fields in biological samples. They optically probe magnetic fields in mammalian cells and tissues with submicron resolution and nanotesla sensitivity using NV diamond magnetometry, and combine the measurements with simulations of nuclear spin precession to predict the corresponding MRI contrast. They demonstrate this in an in vitro model of macrophage iron uptake and in histological samples from a mouse model of hepatic iron overload, and they follow magnetic particle endocytosis in live cells. They say the approach bridges a gap between an MRI voxel and its microscopic constituents. This is a research method, and the abstract describes no clinical use.

What about the third source?

A 2013 Biophysical Journal article on optical magnetic imaging with NV centres was on the source list, but its page text could not be read here, so nothing in this post is taken from it.

How to read this

The two papers use different samples and different quantities, so their resolutions cannot be compared in a simple ranking. The 400 nanometre figure is the optical-imaging resolution reported for the bacteria experiment, and the nanotesla figure belongs to the 2017 work. All numbers are the authors' own. This post is based on abstracts, and full texts were not checked. For temperature sensing with the same defects, see the separate post on nanodiamond thermometry. It makes no claim about products or medical use.

FAQ

What is an NV centre?

A defect in diamond whose spin states can be probed optically and which responds to magnetic fields, as used in both papers.

What did the 2013 work image?

Magnetosome chains inside living magnetotactic bacteria, at 400 nanometre resolution.

What sensitivity did the 2017 work report?

Nanotesla sensitivity with submicron resolution in mammalian cells and tissues.

Is this used in hospitals?

Neither abstract says so. Both describe laboratory measurements.