Dynamic nuclear polarization to enhance NMR signal strength with electron nuclear double resonance (ENDOR-DNP)

Lead Research Organisation: University of Warwick
Department Name: Physics

Abstract

Nuclear magnetic resonance (NMR) is an amazingly powerful technique for studying everything from drug molecules to working human brains. The first step in a magnetic resonance experiment is to polarize the spins which is like making many tiny compass needles point in the same direction. However, most NMR experiments are slow because of the small fraction of nuclei which are spin polarized. Electrons are much more easily polarized but the analogous technique, electron paramagnetic resonance (EPR), is only useful for studying those materials with unpaired electron spins. We are developing the equipment to efficiently transfer electron spin polarization to nuclear spins, allowing a wide range of exciting NMR measurements that would not otherwise be possible. This transfer process is called dynamic nuclear polarization (DNP).

Our DNP equipment uses high magnetic fields of up to 14.1 T. This high field allows more nuclei to be resolved in NMR permitting the study of more interesting samples. Progress with DNP at these magnetic fields has been slow because the corresponding frequency for EPR is 397 GHz, which is in the technologically-difficult THz frequency region. However, we have the equipment to generate, control and detect this frequency for EPR and DNP.

Our source of 397 GHz radiation is smaller, more reliable and less expensive than competing technologies, but produces correspondingly less power. The DNP that has been performed in the past uses this power inefficiently so would not be feasible, but we have demonstrated a prototype solution to this problem: by simultaneously driving EPR and NMR in a suitable polarizing agent, highly efficient DNP is possible. This technique is known as electron-nuclear double resonance (ENDOR) and the polarizing agent is a nitrogen atom inside a buckyball: N@C60. Our previous experiments demonstrate the proof-of-principle but we have never tried to use NMR to readout the nuclear polarization. Succeeding in this would show that ENDOR-DNP is useful for NMR and would be an important breakthrough.

Planned Impact

Good for global science
This project will deliver a step-change improvement in the one area of NMR that is deficient: sensitivity. The repercussions would be huge because NMR is already such a versatile tool for chemistry and materials science. This would lead to more progress in NMR studies of solar cells, batteries, fuel cells and catalysts, biochemicals and pharmaceutical products which would help to create the sustainable energy and advanced healthcare society needs. I will continue to organize and assist in the organization of conferences where academics and industry representatives can share their work to ensure societal impact is maximized and wheels are not reinvented.

Good for business
This project could lead to a commercial product for increased NMR sensitivity within 5 five years. DNP-NMR spectrometers are already sold by Bruker for £1 - £2M demonstrating the demand for this. By offering superior sensitivity with much lower costs and lab-space requirements, I hope that ENDOR-DNP will have commercial as well as academic impact. 300 or more NMR machines are sold per year plus ten times as many MRI machines, and around a third of the superconducting magnets are currently made in the UK, in Oxfordshire by Agilent and Siemens. The financial returns for the UK could therefore greatly outweigh the cost of this research project. A UK SME (Thomas Keating) manufactures THz quasi-optic components that are needed for DNP-NMR so they would benefit greatly from widespread use of DNP.

Good for training and outreach
Two PhD students and a PDRA will be trained as part of this research including exposure to industry and soft skills as part of the Integrated Magnetic Resonance Centre for Doctoral Training (iMR CDT). I will continue my science outreach including my work on various Wikipedia pages. I will create videos describing my work to post on my website.

Publications

10 25 50
 
Description We have measured the sharpest electron spin resonance lines ever. This will improve the precision with which these experiments can be performed in future.
Exploitation Route Could improve the precision of future ESR spectra.
Sectors Electronics

 
Description We wrote software to control the equipment which we are making open source
First Year Of Impact 2013
 
Description Bicentennial Scholarship
Amount £4,000 (GBP)
Organisation Australian Bicentennial Scholarships and Fellowships Trust 
Sector Academic/University
Country United Kingdom
Start 04/2014 
End 06/2014
 
Description First Grant
Amount £208,598 (GBP)
Funding ID UF110535 
Organisation The Royal Society 
Sector Academic/University
Country United Kingdom
Start 12/2013 
End 11/2016
 
Description INSPIRE Physical sciences workshop
Amount £44,820 (GBP)
Funding ID EP/M003019/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 08/2014 
End 01/2016
 
Description Responsive Mode
Amount £1,166,350 (GBP)
Funding ID EP/J014664/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 12/2012 
End 11/2015
 
Description Royal Society University Research Fellowship
Amount £560,854 (GBP)
Funding ID UF110535 
Organisation The Royal Society 
Sector Academic/University
Country United Kingdom
Start 11/2012 
End 10/2017
 
Description Collaboration with John Dennis 
Organisation Queen Mary University of London
Country United Kingdom 
Sector Academic/University 
PI Contribution We are developing DNP at high magnetic fields, and the most precise EPR ever
Collaborator Contribution John Dennis made the sample of N@C60
Impact The sharpest EPR resonances ever have been recorded
Start Year 2012