Periodic Reporting for period 1 - SPECTR (Shaping the future of EPR with cryoprobes and superconducting microresonators)
Reporting period: 2022-06-01 to 2025-03-31
SPECTR (Shaping the Future of EPR with Cryoprobes and Superconducting Microresonators) set out to advance the sensitivity of Electron Paramagnetic Resonance (EPR) - a powerful but inherently low-sensitivity technique used to study materials with unpaired electrons, such as free radicals and metal complexes. EPR has applications in a wide range of fields, from biology and chemistry to materials science and quantum technologies. However, its broader use has been limited by its low sensitivity, especially in biological samples or very small quantities of matter.
The project addressed this challenge by developing and applying cutting-edge hardware tools that significantly enhance EPR sensitivity. SPECTR focused on two complementary innovations: the use of cryogenically cooled EPR probeheads (cryoprobes) to boost the spin signal, and highly sensitive superconducting microwave microresonators for measurements of tiny samples. These tools build on recent breakthroughs in cryogenic low-noise amplifiers (LNA) and microresonator technology, originally developed for quantum technologies.
The project addressed this challenge by developing and applying cutting-edge hardware tools that significantly enhance EPR sensitivity. SPECTR focused on two complementary innovations: the use of cryogenically cooled EPR probeheads (cryoprobes) to boost the spin signal, and highly sensitive superconducting microwave microresonators for measurements of tiny samples. These tools build on recent breakthroughs in cryogenic low-noise amplifiers (LNA) and microresonator technology, originally developed for quantum technologies.
The project successfully developed advanced EPR instrumentation and methodologies to significantly enhance the sensitivity of EPR spectroscopy. A family of X- and Q-band EPR cryoprobes was designed and built, incorporating cryogenic LNAs either in an external cryostat or directly within the sample cryostat, allowing flexibility to select the most suitable cryoprobe depending on experimental conditions. These cryoprobes achieved sensitivity improvements approaching the theoretical limits for cryoprobes at cryogenic temperatures, enabling high-power pulsed EPR experiments with dramatically reduced measurement times. The developments prioritized a user-friendly design to ensure broad accessibility and ease of use.
To further push the sensitivity limits of EPR, spiral-shaped planar microresonators made from the high-temperature superconductor YBCO were fabricated using laser lithography. These resonators feature a nanoliter-scale mode volumes that enhances spin sensitivity by concentrating the microwave magnetic field. Using innovative coupling schemes developed within the project, the microresonators were integrated inside standard EPR setups for wide compatibility. The devices demonstrated excellent magnetic field resilience and high Q-factors, achieving spin-number sensitivity gains of up to 1000-fold compared to conventional 3D resonators, as validated through advanced pulsed EPR experiments.
The developed tools were applied to study complex molecular systems, including some with limited sample volumes. Cryoprobe-enabled DEER experiments successfully characterized various biological systems such as molecular scaffolds, membrane proteins in native-like environments, and calcium-binding proteins, revealing new structural insights into their conformations and aggregation behavior. Meanwhile, spiral microresonators enabled pulsed EPR, ESEEM, ENDOR, and DEER experiments on sub-10 nanoliter biological samples, validating the potential of these tools as a robust platform for advanced pulsed EPR studies in challenging systems. These instrumentation advancements and experimental achievements resulted in multiple publications in collaboration with external partners.
To further push the sensitivity limits of EPR, spiral-shaped planar microresonators made from the high-temperature superconductor YBCO were fabricated using laser lithography. These resonators feature a nanoliter-scale mode volumes that enhances spin sensitivity by concentrating the microwave magnetic field. Using innovative coupling schemes developed within the project, the microresonators were integrated inside standard EPR setups for wide compatibility. The devices demonstrated excellent magnetic field resilience and high Q-factors, achieving spin-number sensitivity gains of up to 1000-fold compared to conventional 3D resonators, as validated through advanced pulsed EPR experiments.
The developed tools were applied to study complex molecular systems, including some with limited sample volumes. Cryoprobe-enabled DEER experiments successfully characterized various biological systems such as molecular scaffolds, membrane proteins in native-like environments, and calcium-binding proteins, revealing new structural insights into their conformations and aggregation behavior. Meanwhile, spiral microresonators enabled pulsed EPR, ESEEM, ENDOR, and DEER experiments on sub-10 nanoliter biological samples, validating the potential of these tools as a robust platform for advanced pulsed EPR studies in challenging systems. These instrumentation advancements and experimental achievements resulted in multiple publications in collaboration with external partners.
The SPECTR project has delivered significant advancements that push the sensitivity and versatility of EPR spectroscopy well beyond the current state of the art. Two core technological innovations underpin this progress: the development of highly sensitive EPR cryoprobes and the introduction of superconducting spiral microresonators with simplified and robust coupling schemes. These developments collectively enable enhanced signal-to-noise ratios and broaden the scope of EPR experiments, opening new opportunities in structural biology, materials science, chemistry, and quantum technologies.
The cryoprobe prototypes developed in this project approach the theoretical sensitivity limits, while remaining fully compatible with widely used commercial spectrometers, providing a practical and adaptable solution for the scientific community. Parallel advancements in superconducting microresonators overcome previous technical barriers by simplifying integration and operation, thus making these ultra-sensitive devices easily accessible to EPR laboratories without requiring specialized expertise. Beyond instrumental innovation, the project demonstrated the utility of these tools in studying biologically relevant systems, showcasing how enhanced EPR sensitivity facilitates structural insights in complex molecular systems.
The scientific results generated by the project have been disseminated extensively through peer-reviewed publications, invited talks at international conferences, and seminars targeting both specialist and broader scientific audiences. Outreach activities, including public engagement events and educational visits to the laboratory, have further contributed to raising awareness and understanding of magnetic resonance among the next generation of researchers and the general public.
Significant training was provided to the fellow, including hands-on development of novel instrumentation, advanced experimental methods, and project management skills. Knowledge exchange was actively fostered through secondments and collaborations with leading international partners. These experiences have been instrumental in advancing the career of the fellow, resulting in international recognition, leadership opportunities, professorship at the host institution, and successful acquisition of an ERC Starting Grant.
In conclusion, the SPECTR project has set new benchmarks in EPR sensitivity and applicability, delivering cutting-edge methodologies that can be used to extend the frontiers of different research fields. The combination of innovative instrumentation, scientific insights, and extensive dissemination and training activities establishes a strong foundation for further scientific progress and broad exploitation of the project results.
The cryoprobe prototypes developed in this project approach the theoretical sensitivity limits, while remaining fully compatible with widely used commercial spectrometers, providing a practical and adaptable solution for the scientific community. Parallel advancements in superconducting microresonators overcome previous technical barriers by simplifying integration and operation, thus making these ultra-sensitive devices easily accessible to EPR laboratories without requiring specialized expertise. Beyond instrumental innovation, the project demonstrated the utility of these tools in studying biologically relevant systems, showcasing how enhanced EPR sensitivity facilitates structural insights in complex molecular systems.
The scientific results generated by the project have been disseminated extensively through peer-reviewed publications, invited talks at international conferences, and seminars targeting both specialist and broader scientific audiences. Outreach activities, including public engagement events and educational visits to the laboratory, have further contributed to raising awareness and understanding of magnetic resonance among the next generation of researchers and the general public.
Significant training was provided to the fellow, including hands-on development of novel instrumentation, advanced experimental methods, and project management skills. Knowledge exchange was actively fostered through secondments and collaborations with leading international partners. These experiences have been instrumental in advancing the career of the fellow, resulting in international recognition, leadership opportunities, professorship at the host institution, and successful acquisition of an ERC Starting Grant.
In conclusion, the SPECTR project has set new benchmarks in EPR sensitivity and applicability, delivering cutting-edge methodologies that can be used to extend the frontiers of different research fields. The combination of innovative instrumentation, scientific insights, and extensive dissemination and training activities establishes a strong foundation for further scientific progress and broad exploitation of the project results.