Electron Paramagnetic Resonance (EPR) can be used to study the structure of paramagnetic species and their surrounding environment ranging from angstrom to nanometer scale. Such species, which include radicals and many common metal ions, play a wide-range of roles in important biological processes such as respiration, photosynthesis and oxidative stress. They are often challenging to study with other methods in a specific and sensitive manner. Most importantly, EPR measurements can be performed in complex environments such as the cell cytosol. Such in-cell measurements greatly benefit from the use of high microwave frequencies and high magnetic fields.
The purpose of the DIM ELICIT project is to develop a high-sensitivity high-power pulse 94 GHz EPR spectrometer, optimized for in-cell structural biology. This involved the design and construction of a module to replace an existing commercial one that currently is part of the CEA-Saclay pulsed high-field high frequency EPR spectrometer. The new module consisted of (1.) a 2 W microwave amplifier to increase the excitation power and (2.) a new microwave receiver with high frequency stability.
The design and construction of the module have ended in the summer of 2019. Testing showed that the new module is capable of much higher pulsed excitation powers than the commercial one. Preliminary results show that the new receiver is significantly more stable over long periods (> 24 h) and, under certain conditions, potentially twice as more sensitive, leading to a four-fold decrease in data acquisition time. These changes will dramatically improve the efficiency of data acquisition and, more importantly, broaden the range of possible in-cell biophysical measurements.
In the autumn of 2019, the newly constructed module has been fully incorporated to the spectrometer and is under-going “real-world” day-to-day use and testing.