This project will develop a radically new photonic band-gap resonator technology that would increase sensitivity of Electron Paramagnetic Resonance (EPR) spectroscopy for studies of biological samples. This new technology is envisioned to have a broad applicability across the many fields where EPR is currently employed by biomedical researchers ? from structure and dynamics of biological macromolecules and complexes to microimaging and detecting and characterizing free-radical species. The overreaching goal is to resolve the main bottleneck of EPR instrumentation when applied to liquid aqueous samples ? the natural environment in which biological molecules and cells perform their functions. The main problem of studying such samples by EPR is a non-resonant absorption of the mm-wave field by water that ultimately limits the volume of EPR sample and also is a cause for microwave heating. These problems only worsen as the EPR resonant frequency increases with the magnetic field, thereby adversely affecting any gain in sensitivity potentially attainable with field/high frequency EPR ?an emerging method with superior spectral resolution. The primary objective of this exploratory research grant is to demonstrate that one-dimensional photonic band-gap structures are suitable for an effective separation of the electrical and magnetic field components of mm-waves while achieving exceptionally high quality factors Q=500-1,000 even with lossy aqueous samples with volumes of at least several microliters. It is hypothesized that the proposed structures will maximize the product of Q and the resonator filling factor while yielding at least an order in magnitude improvement in EPR sensitivity vs. state-of-the-art. The approach involves both electromagnetic simulations and constructing a W-band (95 GHz) photonic band-gap resonator for CW EPR and testing its performance for a series of biomolecules labeled with nitroxides and Gd(III) ions. Further, the design will be optimized for pulsed EPR and then scaled up to ca. 190- 200 GHz resonant frequency. This project is viewed as a first step towards further expanding the applicability of high-field/high-frequency EPR in NIH research. Future directions of this project will utilize large sample volume of photonic band-gap resonators for their integration with dynamic nuclear polarization (DNP) instrumentation for a dramatic enhancement of NMR signals at physiologically relevant conditions and temperatures, including membrane proteins in native lipid bilayers, cellular organelles, and, potentially, living cells.
A novel type of photonic band-gap resonators, that will dramatically increase the sensitivity and broaden utilization of Electron Paramagnetic Resonance (EPR) spectroscopy in structural and dynamical studies of biological samples, will be developed. The goal is to resolve the main bottleneck of high-field EPR when applied to liquid aqueous samples ? absorption of microwave field by water that limits the volume of EPR sample and causes microwave heating. The primary objective of this exploratory research grant is to design, build, and optimize one-dimensional photonic band-gap structures for achieving exceptionally high quality factors even with lossy aqueous samples having volumes of at least several microliters.
| Milikisiyants, Sergey; Nevzorov, Alexander A; Smirnov, Alex I (2018) Photonic band-gap resonators for high-field/high-frequency EPR of microliter-volume liquid aqueous samples. J Magn Reson 296:152-164 |
