ESR Microscopy and Nanoscopy with “Induction” Detection

Abstract

The current state‐of‐the‐art in the fields of Nuclear Magnetic Resonance (NMR) and Electron Spin Resonance (ESR) micro‐imaging is reviewed. Special attention is given to the uniqueness and the advantages of the conventional “induction” detection method with respect to other emerging sensitive magnetic resonance detection and imaging techniques. Following this, a theoretical description of the factors affecting the sensitivity and resolution in induction detection ESR is provided. Based on the theory, new approaches to substantially improve ESR capabilities, both at room temperature and at low cryogenic temperatures, are discussed. Representative results of experiments conducted at room temperature and at frequencies of 10–16 GHz show that with test samples, a sensitivity of ∼107 electron spins and a resolution of ∼3 microns are currently available. The results confirm the validity of the theoretical approach and confirm the value of striving for even higher frequencies and lower temperatures, in order to further improve the performance Finally, some of the current and potential applications of ESR microscopy and nanoscopy (involving imaging with a resolution of ∼100 nm or better) are presented.

Scanned-probe detection of electron spin resonance from a nitroxide spin probe

“…For macromolecules too large to characterize by NMR or X-ray diffraction, the tertiary structure of proteins (1)(2)(3), nucleic acids (4,5), and biomolecular assemblies (6,7) can be explored by using inductively-detected electron spin resonance (ESR) to measure distances between pairs of attached spin labels (2-5, 7, 8). These studies, however, require bulk quantities of sample (9) and demand multiple experiments with spin labels attached to different locations in the target macromolecule. Mechanical detection and imaging of single-electron spins has been demonstrated, in E centers in gamma-irradiated quartz (10), and it is natural to explore applying magnetic resonance force microscopy (MRFM) (11)(12)(13)(14)(15) to map the locations of individual spin labels attached to a single biomacromolecule.…”

ESR Microscopy for Biological and Biomedical Applications

“…, a home-built pulsed MW bridge, a home-built high current pulse gradient driver with high voltage pre-regulator, a timing card, a signal digitizer, imaging probes, and a high-homogeneity electromagnet with field-frequency lock. 10,11, 21 In the imaging probe, a double stacked dielectric resonator was nested inside a 3-dimensional set of magnetic field gradient coils. The X gradient coil is a standard Maxwell pair, and the Y, Z gradient coils are of Golay design.…”

“…Sample specimens are sealed in a flat or cylindrical holder that is inserted between the resonators for imaging. Further descriptions of the basic instrumentation systems can be found elsewhere, 10,11,22 therefore only key system upgrades will be described here.…”

“…7,8,9 Furthermore, high resolution pulsed ESR microscopy (ESRM) has been developed by Blank, Freed and co-workers using a high Q dielectric resonator at higher frequencies of 9 and 16 GHz. 10, 11,12 High resolution ESRM can detect ~10 7 spins with resolution of a few microns in about an hour, which is ~5 orders of magnitude better than conventional NMR microscopy with micro coil detection. 10 This is mainly due to the much larger dipole moment of the electron spin, the high quality factor of the resonator and application of advanced MW technology and devices.…”

Fourier Transform EPR Spectroscopy of Trityl Radicals for Multifunctional Assessment of Chemical Microenvironment

“…[17,18] This unique multifunctional sensitivity of the p 1 TAM probe decreases the method invasiveness and will allow for a better correlation of the parameters independent of the distribution of the probe. The demonstrated FT-EPR application can be extended to imaging modalities [19][20][21] taking into account the simple EPR spectrum and long relaxation times of the p 1 TAM probe (Table 1). FT-EPR spectra of 0.2 mM p 1 TAM measured in 150 mM NaCl aqueous solutions at different Na-phosphate buffer concentrations, pH 6.53.…”