EPR Microscopy

EPR is a powerful methodology for characterizing paramagnetic species but has the limitation that it primarily involves the use of homogenous samples in a test tube. For heterogenous samples one must resort to the use of spatially resolved methodologies, which are commercially available, but limited in their resolution to the millimeter scale. Recent years have witnessed the development of EPR microscopy, a complementary EPR imaging methodology that is carried out with mm-scale samples and reaches micron and even submicron-scale spatial resolution. This approach involves the use of advanced high-sensitivity EPR micro-resonators, large magnetic field gradients to spatially encode the EPR signal, and advanced pulse spectrometer software to control and execute the imaging sequences and process the image data. This article describes the theoretical basis and the experimental methodological developments of EPR microscopy and lists its primary applications, accompanied by some specific recent examples.