Prawer/Bar-Gill joint PhD projects

Prof Steven Prawer & Prof Nir Bar-Gill

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

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

https://physics.unimelb.edu.au/home

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

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

https://bargill.phys.huji.ac.il/

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

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

 

Project 1: Home base – UoM

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

 

Project 2: Home base – HUJI

Diamond sensor for Reactive Oxygen Species (ROS)

Reactive Oxygen Species (ROS), and radicals in general, play a fundamental role in a broad range of chemical and biological processes, usually as catalysts and mediators of various reactions. For example, ROS are crucial as catalysts in clean energy production, such as batteries and light-harvesting complexes, and are instrumental in cellular and inter-cellular disease processes, such as inflammation. Detecting and quantifying ROS dynamics is a challenging task, as these molecules are usually short-lived due to their catalytic behavior. This is usually achieved by using spin traps or modified fluorescence markers, which act as indirect indications of ROS activity. However, due to the need to introduce them into the biological system and since they are essentially side-effects of the reactive process, the resulting measurements can affect the process itself, and their quantitative analysis is limited. The proposed project is based on the fact these radicals have free spins, and therefore introduce magnetic noise into the environment. Such noise can be detected and characterized by the diamond-NV platform, through various control schemes referred to as noise spectroscopy.

Figure 3: Schematic for noise spectroscopy schemes based on CPMG and DYSCO: green indicates a laser pulse, orange indicates a π or π/2 pulse, while yellow and blue indicate microwave-pulse blocks composed of 4π pulses with the denoted phases (in which ϕ is a function of the block number).

In this project we will realize a biologically compatible noise spectroscopy system for studying ROS dynamics:

• Develop and optimize noise spectroscopy schemes relevant for ROS measurements, such as we have demonstrated recently using continuous and pulsed control. For this purpose, we will benefit from a collaboration with Uri Banin of the Chemistry Dept. at HUJI, who provides us with specifically designed nano-particles that controllably create ROS as a function of optical illumination (using 405nm light).

• Optimize diamond substrate for these measurements in terms of various parameters, including diamond structure and nanofabrication, NV integration, optical coupling.

• Construct an integrated, biologically compatible ROS sensor, and demonstrate measurements of ROS concentration as a function of controlled stimuli. The proposed project will combine the expertise of the Prawer group in terms of the diamond structure and NV integration, with the noise spectroscopy expertise of the BarGill group (including the collaboration with the Banin group).

 

Year 1: HUJI – develop and optimize the relevant noise spectroscopy schemes

Year 2: UoM – learn and fabricate optimized NV-containing diamond samples

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