Towards Nanometer Resolution Single Particle Imaging by Mechanically Detected Magnetic Resonance

“Towards Nanometer Resolution Single Particle Imaging  by Mechanically Detected Magnetic Resonance”

John A. Marohn, Ph.D. – Professor, Department of Chemistry and Chemical Biology, Cornell University

Imagine being able to carry out nm- or even angstrom-resolution proton imaging of essentially any organic thin-film sample.  Imagine being able to map the locations of single nitroxide-based electron-spin labels at sub-angstrom resolution in order to determine the tertiary structure of individual biomolecules and macromolecular complexes.

Magnetic resonance force microscopy (MRFM) has recently been used to create a three-dimensional map an individual virus’s proton density at 4 to 10 nm resolution [1] and has been used to detect electron spin resonance from single defects in silica [2].  In the experiment of Ref. 1, however, the sample was affixed manually to the leading edge of a fragile high-compliance silicon microcantilever.  Frustratingly, the experiment of Ref. 2 relied on spin-detection protocols with stringent sample relaxation-time requirements that are, unfortunately, not met by widely used electron-spin labels such as nitroxides.

In this short talk I will show magnetic-tipped cantilevers and new spin-detection protocols that we have developed that promise to make magnetic resonance force microscopy applicable to essentially any (frozen, in vacuum) thin-film sample.   We recently reported a force-gradient based approach to mechanically detecting electron spin resonance from a nitroxide spin label widely used to study the tertiary structure of proteins, DNA, and RNA [3].  I present evidence of transfer of polarization from this TEMPAMINE nitroxide radical to surrounding deuterium spins in a magnetic resonance force microscope experiment [4]. We have developed attonewton sensitivity cantilevers with integral nickel [5] and cobalt nanomagnets and, in collaboration with IBM Alamden, have used these cantilevers to detect NMR at a few hundred proton sensitivity [6].