Nanoscale Spin Hypepolarization and Imaging
Abstract
A Cornell-IBM collaborative experiment recently used an attonewton-sensitivity cantilever with a nanomagnetic tip to detect nuclear magnetic resonance at 500 proton sensitivity [Longenecker, et al., Marohn, ACS Nano, 2012, 6:9637, URL http://dx.doi.org/10.1021/nn3030628]. This demonstration opens the door to using magnetic resonance force microscopy to acquire few-nanometer-resolution magnetic resonance images of a wide array of samples. Over the last four years, the P.I. and his team have created a versatile, scanned-probe, cryogenic magnetic resonance force microscope to capitalize on this advance. This microscope, developed with ARO funding, is capable of harnessing the Cornell magnet-tipped cantilevers in a cryogenic imaging experiment. The unique capabilities of the microscope are apparent in our recently published experiment demonstrating microwave-induced dynamic nuclear polarization in a magnetic resonance force microscope experiment for the first time [Isaac, et al., Marohn, Phys. Chem. Chem. Phys., 2016, 18:8806, URL http://dx.doi.org/10.1039/C6CP00084C]. The goal of this proposal is to harness dynamic nuclear polarization to create hyperpolarized nuclear magnetization for use in a magnetic resonance force microscope imaging experiment. Here we show that employing hyperpolarized nuclear magnetization in a magnetic resonance force microscope experiment has the potential to significantly increase the signal-to-noise ratio of the experiment. To achieve this goal, a stepwise plan of experiments is introduced involving polymers and biomolecules doped with nitroxide free radicals. Experiments are proposed to detect nuclear magnetic resonance from small-ensemble magnetization fluctuations; to observe electron spin resonance by detecting Curie-law magnetization from small numbers of electron spins; to implement cantilever shuttling experiments to adjust the cantilever tip s magnetic field gradient during dynamic nuclear polarization; and to detect and image nuclear magnetic resonance signal from hyperpolarized proton spins. Three dynamic nuclear polarization mechanisms will be evaluated for use in magnetic resonance force microscopy: the cross effect, the NOVEL effect, and the recently proposed separative magnetization transport hyperpolarization mechanism. The proposed experiments will be operating in a new regime where the applied magnetic field gradients and radiofrequency irradiation will be large enough to create well-defined, adjustable, atomic-scale gradients in spin polarization. Working in this limit represents an exciting opportunity to significantly expand our microscopic understanding of spin diffusion and hyperpolarization techniques such as dynamic nuclear polarization and separative magnetization transport. The proposed experiments are clearly a fertile ground for exploring the behavior of coupled electron and nuclear spin magnetization far from equilibrium. Taken together, the experiments proposed below will lay the groundwork for applying magnetic resonance force microscopy to image individual copies of macromolecules and biological assemblies at nanometer-scale resolution.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Oct 17, 2018
- Source ID
- W911NF1710247
Entities
People
- John A Marohn
Organizations
- Army Contracting Command
- Cornell University
- United States Army