Scanned-probe detection of electron spin resonance from a nitroxide spin probe.
We report an approach that extends the applicability of ultrasensitive force-gradient detection of magnetic resonance to samples with spin-lattice relaxation times (T (1)) as short as a single cantilever period. To demonstrate the generality of the approach, which relies on detecting either cantilever frequency or phase, we used it to detect electron spin resonance from a T (1) = 1 ms nitroxide spin probe in a thin film at 4.2 K and 0.6 T. By using a custom-fabricated cantilever with a 4 microm-diameter nickel tip, we achieve a magnetic resonance sensitivity of 400 Bohr magnetons in a 1 Hz bandwidth. A theory is presented that quantitatively predicts both the lineshape and the magnitude of the observed cantilever frequency shift as a function of field and cantilever-sample separation. Good agreement was found between nitroxide T (1) 's measured mechanically and inductively, indicating that the cantilever magnet is not an appreciable source of spin-lattice relaxation here. We suggest that the new approach has a number of advantages that make it well suited to push magnetic resonance detection and imaging of nitroxide spin labels in an individual macromolecule to single-spin sensitivity.
Moore
Eric W
EW
Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853-1301, USA.
Lee
SangGap
S
Hickman
Steven A
SA
Wright
Sarah J
SJ
Harrell
Lee E
LE
Borbat
Peter P
PP
Freed
Jack H
JH
Marohn
John A
JA
D055592:Biophysical Phenomena; D003497:Cyclic N-Oxides / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data; D004867:Equipment Design; D009682:Magnetic Resonance Spectroscopy; D008872:Microwaves; D015394:Molecular Structure; D013113:Spin Labels; D013816:Thermodynamics
D003497:Cyclic N-Oxides; D013113:Spin Labels; C015527:4-amino-TEMPO