A frequency-swept longitudinal detection (LOD) EPR system is described for ultra-low field spectroscopy and relaxometry. With the capability of performing simultaneous transmit and receive with −80 dB isolation, this LOD-EPR can capture signals with decay constants in the nanosecond range and in theory even sub-nanosecond range, at fields close to the earth's magnetic field. The theoretical principles underlying this LOD-EPR are based on a fictitious field that accounts for the Z-axis magnetization polarized by a radiofrequency field alone. The electron spin relaxation time is obtained directly from a previously derived equation that describes the relationship between the relaxation time and the spectral peak position. Herein, the first frequency-swept LOD-EPR system is described in detail, along with experimental measurements of the short relaxation time (∼30 ns) of the free radical, 2,2-diphenyl-1-picrylhydrazyl, at zero to low field.
Bibliographical noteFunding Information:
This research has been supported by the National Institutes of Health [grants U01 EB025153 and P41 EB027061], and the Malcolm B. Hanson Endowed Chair in Radiology. The authors would like to thank Steven Jungst, Jerahmie Radder, and Russell Lagore for their technical support. We are also grateful to Efraín Torres and Lance DelaBarre for valuable discussions and their inspiring thoughts.
© 2022 Elsevier Inc.
- Electron spin relaxation time
- Frequency-swept EPR
- Longitudinal detection
- Simultaneous transmit and receive
PubMed: MeSH publication types
- Journal Article