Cell-scale MRI

Nuclear magnetic resonance (NMR) is an indispensable characterization technique, extensively used in chemical analysis, as well as in other fields (biology, physics). The imaging modality of this scheme, magnetic resonance imaging (MRI), has unparalleled capabilities in varied fields, and notably in biological and medical diagnostics. In essence, MRI uses pickup coils to measure magnetic signals generated by nuclear spins within the sample (usually from water molecules within our body in the medical case). Despite its obvious usefulness, the sensitivity and resolution of the measurement coils are insufficient to explore cellular-scale signals. Over the past decade, localized defects in diamond, namely nitrogen-vacancy (NV) color centers, have emerged as a promising platform for magnetic sensing. In short, the NV spin is sensitive to external magnetic fields, and can be readout optically, e.g. using a camera. While magnetic sensing can be relevant to many different applications, it has been demonstrated also in the context of MRI signals, and in certain cases achieved improved sensitivity and resolution compared to the standard MRI approach.
In this proposed project, led by the Prawer group from UoM, we will develop an integrated diamond chip suitable for deployment in a diamond-based MRI system, aimed at detecting MRI signals on the cellular level. Based on an optical magnetic microscope concept (see Figure 1), we will optimize the various aspects of the system for the cellular MRI goal: As can be seen below, the discrete component parts of such a system are well known. However, integration of all the components on a single chip which would allow for easy deployment in biological environments, has not yet been accomplished. This project, based on nanofabrication techniques developed at UoM, will aim to for such integration and early demonstration of sensitivity in in-vitro operation.

Figure 1: Custom-built Wide-field magnetic imaging microscope. The sample is placed on the surface of a diamond chip, which is implanted with a high density thin layer of NV centers near the surface. The diamond is attached to the cover-slip using immersion oil which is glued to the holder. Optical pumping green laser is incident through the bottom-polished side of the diamond surface using the objective in EPI mode. Coherent MW-field manipulation, which is created by an MW antenna, is located near the diamond surface containing the NV layer. The NV fluorescence passes through the diamond, the cover-slip and the dichroic mirror and is then imaged onto a camera using the objective and a tube lens.

The lead PhD candidate will:

• Optimize diamond chip in terms of thickness, either improving imaging resolution using ultrathin diamond chips (pioneered by the Prawer group), or thick diamond slabs allowing for side illumination (thus reducing potential adverse effects of illumination on the samples.

• Optimize NV center layer, in terms of quantum coherence properties, density, and depth. Through the expertise of the Prawer group we will consider approaches including ion implantation, delta-doping and overgrowth, surface termination and more.

• Optimize sensing protocols, based on commonly used MRI sequences and experiments performed using NVs. Study the effects of hyper-polarization schemes for enhanced sensitivity, in the context of realistic samples (e.g. might not be beneficial in scenarios involving fast diffusion). For example, a novel low magnetic field hyper-polarization protocol was recently introduced by us.

Figure 2: schematic of the low-magnetic field hyper-polarization scheme, named rNOVEL (refocused NOVEL), as it combines polarization transfer under the resonant Hartmann-Hahn condition with strong dynamical decoupling pulses.


Year 1: UoM – optimize the diamond substrate, nanofabrication and NV integration

Year 2: HUJI – learn and implement the MRI sensing techniques relevant for cellular MRI

Year 3: UoM – construct the system and perform initial measurements


Supervision Team:

UoM Prof Steven Prawer: s.prawer@unimelb.edu.au

School of Physics, Faculty of Science, The University of Melbourne


HUJI Prof Nir Bar-Gill: bargill@phys.huji.ac.il

The Racah Institute of Physics, Faculty of Science, Hebrew University of Jerusalem


HUJI co-supervisor Prof Alex Retzker: retzker@phys.huji.ac.il

The Racah Institute of Physics, Faculty of Science, Hebrew University of Jerusalem