title: Scanned-probe detection of electron spin resonance from a nitroxide spin probe.
abstract: 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.
authors.affiliation: Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853-1301, USA.
authors.forename: Eric W
authors.initials: EW
authors.lastname: Moore
authors.forename: SangGap
authors.initials: S
authors.lastname: Lee
authors.forename: Steven A
authors.initials: SA
authors.lastname: Hickman
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Wright
authors.forename: Lee E
authors.initials: LE
authors.lastname: Harrell
authors.forename: Peter P
authors.initials: PP
authors.lastname: Borbat
authors.forename: Jack H
authors.initials: JH
authors.lastname: Freed
authors.forename: John A
authors.initials: JA
authors.lastname: Marohn
mesh_terms: 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
chemical_list: D003497:Cyclic N-Oxides; D013113:Spin Labels; C015527:4-amino-TEMPO