Biochemists can use electron paramagnetic resonance (EPR) on protein single crystals to determine the ultimate electronic structure of paramagnetic protein intermediates and investigate the relative magnetic tensor to a molecular structure. The method is, however, withheld by typical protein crystal dimensions (0.05 to 0.3 mm) that do not provide sufficient signal intensity during protein crystallography. In a new study on Science Advances, Jason W. Sidabras and an interdisciplinary research team in the departments of Chemical Energy Conversion, Photobiotechnology, Institute for Biology and Experimental Physics in Germany presented a microwave self-resonant microhelix to quantify nanoliter samples. The scientists implemented the technique in a commercial X-band (mid-range frequency; 9.5 GHz) EPR spectrometer. The self-resonant microhelix provided a measured signal-to-noise improvement compared to other commercial EPR resonators. The work enables advanced EPR techniques to study protein single crystals for X-ray crystallography, without size-related exclusions or challenges. To demonstrate the method, Sidabras et al. used single crystal protein [FeFe]-hydrogenase (from Clostridiu...