Improved EPR sensitivity for aqueous biological samples using low-volume multi-channel cells and dielectric resonators. bioRxiv 2025 Jun 07
Date
06/12/2025Pubmed ID
40501798Pubmed Central ID
PMC12157622DOI
10.1101/2025.06.03.657726Abstract
Reducing sample volumes for electron paramagnetic resonance (EPR) spectroscopy applications places increasing demands on hardware design to preserve or enhance EPR signal intensity. In this work, the design, fabrication, and testing of dielectric resonators and multi-channel aqueous sample cells for applications in X-band (nominally 9.5 GHz) EPR is presented. Our aim was to maximize the EPR signal intensity for sample sizes of 3-4 μL and 200 nL. These advances are summarized as follows: single-crystal sapphire and rutile dielectric resonators with very low loss tangent and high resonator efficiency; minimum dielectric resonator coupling to radiation shield to reduce ohmic losses; 3D printed aqueous sample cells with thin multi-channel construction to minimize radio-frequency dissipation in the sample; and a Gordon coupler for maximum coupling range and minimum stored energy to eliminate frequency shifts during tuning. Sample cell geometries were designed by leveraging insights gained from analytic theory to inform finite-element modeling of electromagnetic fields. Experimental comparisons of multi-channel sample cells using a sapphire resonator exhibited a 2.2-fold increase in EPR signal intensity compared with a standard capillary at 3-4 μL, while simulations predict an additional 23% improvement with further 3D printing advances. For samples at 200 nL, a rutile dielectric resonator with a multi-channel sample cell was simulated to improve EPR sensitivity by a 2.7-fold increase compared with a capillary at the same volume.
Author List
Mett RR, Garces AM, Anilkumar A, Wehrley JT, Lerch MT, Klug CS, Sidabras JWAuthors
Alexander M. Garces Postdoctoral Researcher in the Biophysics department at Medical College of WisconsinCandice S. Klug PhD Professor in the Biophysics department at Medical College of Wisconsin
Michael Lerch PhD Associate Professor in the Biophysics department at Medical College of Wisconsin
Jason W. Sidabras PhD Assistant Professor in the Biophysics department at Medical College of Wisconsin
