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Cho FH, Park J, Oh S, Yu J, Jeong Y, Colazzo L, Spree L, Hommel C, Ardavan A, Boero G, Donati F. A continuous-wave and pulsed X-band electron spin resonance spectrometer operating in ultra-high vacuum for the study of low dimensional spin ensembles. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2024; 95:063904. [PMID: 38864723 DOI: 10.1063/5.0189974] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/02/2023] [Accepted: 05/09/2024] [Indexed: 06/13/2024]
Abstract
We report the development of a continuous-wave and pulsed X-band electron spin resonance (ESR) spectrometer for the study of spins on ordered surfaces down to cryogenic temperatures. The spectrometer operates in ultra-high vacuum and utilizes a half-wavelength microstrip line resonator realized using epitaxially grown copper films on single crystal Al2O3 substrates. The one-dimensional microstrip line resonator exhibits a quality factor of more than 200 at room temperature, close to the upper limit determined by radiation losses. The surface characterizations of the copper strip of the resonator by atomic force microscopy, low-energy electron diffraction, and scanning tunneling microscopy show that the surface is atomically clean, flat, and single crystalline. Measuring the ESR spectrum at 15 K from a few nm thick molecular film of YPc2, we find a continuous-wave ESR sensitivity of 2.6 × 1011 spins/G · Hz1/2, indicating that a signal-to-noise ratio of 3.9 G · Hz1/2 is expected from a monolayer of YPc2 molecules. Advanced pulsed ESR experimental capabilities, including dynamical decoupling and electron-nuclear double resonance, are demonstrated using free radicals diluted in a glassy matrix.
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Affiliation(s)
- Franklin H Cho
- Center for Quantum Nanoscience, Institute for Basic Science, Seoul 03760, South Korea
- Ewha Womans University, Seoul 03760, South Korea
| | - Juyoung Park
- Center for Quantum Nanoscience, Institute for Basic Science, Seoul 03760, South Korea
- Department of Physics, Ewha Womans University, Seoul 03760, South Korea
| | - Soyoung Oh
- Center for Quantum Nanoscience, Institute for Basic Science, Seoul 03760, South Korea
- Department of Physics, Ewha Womans University, Seoul 03760, South Korea
| | - Jisoo Yu
- Center for Quantum Nanoscience, Institute for Basic Science, Seoul 03760, South Korea
- Department of Physics, Ewha Womans University, Seoul 03760, South Korea
| | - Yejin Jeong
- Center for Quantum Nanoscience, Institute for Basic Science, Seoul 03760, South Korea
- Department of Physics, Ewha Womans University, Seoul 03760, South Korea
| | - Luciano Colazzo
- Center for Quantum Nanoscience, Institute for Basic Science, Seoul 03760, South Korea
- Ewha Womans University, Seoul 03760, South Korea
| | - Lukas Spree
- Center for Quantum Nanoscience, Institute for Basic Science, Seoul 03760, South Korea
- Ewha Womans University, Seoul 03760, South Korea
| | - Caroline Hommel
- Center for Quantum Nanoscience, Institute for Basic Science, Seoul 03760, South Korea
- Ewha Womans University, Seoul 03760, South Korea
| | - Arzhang Ardavan
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU, United Kingdom
| | - Giovanni Boero
- Microsystems Laboratory, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne 1015, Switzerland
| | - Fabio Donati
- Center for Quantum Nanoscience, Institute for Basic Science, Seoul 03760, South Korea
- Department of Physics, Ewha Womans University, Seoul 03760, South Korea
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2
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Dayan N, Artzi Y, Jbara M, Cristea D, Blank A. Pulsed Electron-Nuclear Double Resonance in the Fourier Regime. Chemphyschem 2022; 24:e202200624. [PMID: 36464644 DOI: 10.1002/cphc.202200624] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2022] [Revised: 11/24/2022] [Accepted: 12/01/2022] [Indexed: 12/11/2022]
Abstract
Nuclear magnetic resonance (NMR) spectroscopy provides atomic-level molecular structural information. However, in molecules containing unpaired electron spins, NMR signals are difficult to measure directly. In such cases, data is obtained using the electron-nuclear double resonance (ENDOR) method, where nuclei are detected through their interaction with nearby unpaired electron spins. Unfortunately, electron spins spread the ENDOR signals, which challenges current acquisition techniques, often resulting in low spectral resolution that provides limited structural details. Here, we show that by using miniature microwave resonators to detect a small number of electron spins, integrated with miniature NMR coils, one can excite and detect a wide bandwidth of ENDOR data in a single pulse. This facilitates the measurement of ENDOR spectra with narrow lines spread over a large frequency range at much better spectral resolution than conventional approaches, which helps reveal details of the paramagnetic molecules' chemical structure that were not accessible before.
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Affiliation(s)
- Nir Dayan
- Schulich Faculty of Chemistry, Technion - Israel Institute of Technology, 3200003, Haifa, Israel
| | - Yaron Artzi
- Schulich Faculty of Chemistry, Technion - Israel Institute of Technology, 3200003, Haifa, Israel
| | - Moamen Jbara
- Schulich Faculty of Chemistry, Technion - Israel Institute of Technology, 3200003, Haifa, Israel
| | - David Cristea
- Schulich Faculty of Chemistry, Technion - Israel Institute of Technology, 3200003, Haifa, Israel
| | - Aharon Blank
- Schulich Faculty of Chemistry, Technion - Israel Institute of Technology, 3200003, Haifa, Israel
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3
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Abhyankar N, Agrawal A, Campbell J, Maly T, Shrestha P, Szalai V. Recent advances in microresonators and supporting instrumentation for electron paramagnetic resonance spectroscopy. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2022; 93:101101. [PMID: 36319314 PMCID: PMC9632321 DOI: 10.1063/5.0097853] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/02/2022] [Accepted: 08/13/2022] [Indexed: 06/16/2023]
Abstract
Electron paramagnetic resonance (EPR) spectroscopy characterizes the magnetic properties of paramagnetic materials at the atomic and molecular levels. Resonators are an enabling technology of EPR spectroscopy. Microresonators, which are miniaturized versions of resonators, have advanced inductive-detection EPR spectroscopy of mass-limited samples. Here, we provide our perspective of the benefits and challenges associated with microresonator use for EPR spectroscopy. To begin, we classify the application space for microresonators and present the conceptual foundation for analysis of resonator sensitivity. We summarize previous work and provide insight into the design and fabrication of microresonators as well as detail the requirements and challenges that arise in incorporating microresonators into EPR spectrometer systems. Finally, we provide our perspective on current challenges and prospective fruitful directions.
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Affiliation(s)
| | - Amit Agrawal
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - Jason Campbell
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - Thorsten Maly
- Bridge12 Technologies, Inc., Natick, Massachusetts 01760, USA
| | | | - Veronika Szalai
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
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Teucher M, Sidabras JW, Schnegg A. Milliwatt three- and four-pulse double electron electron resonance for protein structure determination. Phys Chem Chem Phys 2022; 24:12528-12540. [PMID: 35579184 DOI: 10.1039/d1cp05508a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Electron paramagnetic resonance (EPR) experiments for protein structure determination using double electron-electron resonance (DEER) spectroscopy rely on high-power microwave amplifiers (>300 W) to create the short pulse lengths needed to excite a sizable portion of the spectrum. The recently introduced self-resonant microhelix combines a high B1 conversion efficiency with an intrinsically large bandwidth (low Q-value) and a high absolute sensitivity. We report dead times in 3-pulse DEER experiments as low as 14 ± 2 ns achieved using less than 1 W of power at X-band (nominally 9.5 GHz) for experiments on a molecular ruler and a T4 lysozyme sample for concentrations down to 100 μM. These low-power experiments were performed using an active volume 120 times smaller than that of a standard pulse EPR resonator, while only a 11-fold decrease in the signal-to-noise ratio was observed. Small build sizes, as realized with the microhelix, give access to volume-limited samples, while shorter dead times allow the investigation of fast relaxing spin species. With the significantly reduced dead times, the 3-pulse DEER experiment can be revisited. Here, we show experimentally that 3-pulse DEER offers superior sensitivity over 4-pulse DEER. We assert that the microhelix paves the road for low-cost benchtop X-band pulse EPR spectrometers by eliminating the need for high-power amplifiers, accelerating the adoption of pulse EPR to a broader community.
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Affiliation(s)
- Markus Teucher
- EPR Research Group, Max Planck Institute for Chemical Energy Conversion, Stift-straße 34-36, Mülheim an der Ruhr, 45470, Germany.
| | - Jason W Sidabras
- EPR Research Group, Max Planck Institute for Chemical Energy Conversion, Stift-straße 34-36, Mülheim an der Ruhr, 45470, Germany.
| | - Alexander Schnegg
- EPR Research Group, Max Planck Institute for Chemical Energy Conversion, Stift-straße 34-36, Mülheim an der Ruhr, 45470, Germany.
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Rane V. Harnessing Electron Spin Hyperpolarization in Chromophore-Radical Spin Probes for Subcellular Resolution in Electron Paramagnetic Resonance Imaging: Concept and Feasibility. J Phys Chem B 2022; 126:2715-2728. [PMID: 35353514 DOI: 10.1021/acs.jpcb.1c10920] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Obtaining a subcellular resolution for biological samples doped with stable radicals at room temperature (RT) is a long-sought goal in electron paramagnetic resonance imaging (EPRI). The spatial resolution in current EPRI methods is constrained either because of low electron spin polarization at RT or the experimental limitations associated with the field gradients and the radical linewidth. Inspired by the recent demonstration of a large electron spin hyperpolarization in chromophore-nitroxyl spin probe molecules, the present work proposes a novel optically hyperpolarized EPR imaging (OH-EPRI) method, which combines the optical method of two-photon confocal microscopy for hyperpolarization generation and the rapid scan (RS) EPR method for signal detection. An important aspect of OH-EPRI is that it is not limited by the abovementioned restrictions of conventional EPRI since the large hyperpolarization in the spin probes overcomes the poor thermal spin polarization at RT, and the use of two-photon optical excitation of the chromophore naturally generates the required spatial resolution, without the need for any magnetic field gradient. Simulations based on time-dependent Bloch equations, which took into account both the RS field modulation and the hyperpolarization generation by optical means, were performed to examine the feasibility of OH-EPRI. The simulation results revealed that a spatial resolution of up to 2 fL can be achieved in OH-EPRI at RT under in vitro conditions. Notably, the majority of the requirements for an OH-EPRI experiment can be fulfilled by the currently available technologies, thereby paving the way for its easy implementation. Thus, the proposed method could potentially bridge the sensitivity gap between the optical and magnetic imaging techniques.
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Affiliation(s)
- Vinayak Rane
- Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India
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Artzi Y, Yishay Y, Fanciulli M, Jbara M, Blank A. Superconducting micro-resonators for electron spin resonance - the good, the bad, and the future. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2022; 334:107102. [PMID: 34847488 DOI: 10.1016/j.jmr.2021.107102] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2021] [Revised: 08/17/2021] [Accepted: 10/30/2021] [Indexed: 06/13/2023]
Abstract
The field of electron spin resonance (ESR) is in constant need of improving its capabilities. Among other things, this means having better resonators to reach improved spin sensitivity and enable larger microwave-power-to-microwave-magnetic-field conversion factors. Surface micro-resonators, made of small metallic patches on a dielectric substrate, provide very good absolute spin sensitivity and high conversion factors due to their very small mode volume. However, such resonators suffer from relatively low spin concentration sensitivity and a low-quality factor, a fact that offsets some of their significant potential advantages. The use of superconducting patches to replace the metallic layer seems a reasonable and straightforward solution to the quality factor issue, at least for measurements carried out at cryogenic temperatures. Nevertheless, superconducting materials, especially those that can operate at moderate cryogenic temperatures, are not easily incorporated into setups requiring high magnetic fields due to the electric current vortices generated in the latter's surface. This makes the transition from normal conducting materials to superconductors highly nontrivial. Here we present the design, fabrication, and testing results of surface micro-resonators made of yttrium barium copper oxide (YBCO), a superconducting material that operates also at high magnetic fields and makes it possible to pursue ESR at moderate cryogenic temperatures (up to ∼ 80 K). We show that with a unique experimental setup, these resonators can be made to operate well even at high fields of ∼ 1.2 T. Furthermore, we analyze the effect of current vortices on the ESR signal and the spins' coherence times. Finally, we provide a head-to-head comparison of YBCO vs copper resonators of the same dimensions, which clearly shows their pros and cons and directs us to future potential developments and improvements in this field.
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Affiliation(s)
- Yaron Artzi
- Schulich Faculty of Chemistry, Technion - Israel Institute of Technology, Haifa 3200003, Israel
| | - Yakir Yishay
- Schulich Faculty of Chemistry, Technion - Israel Institute of Technology, Haifa 3200003, Israel
| | - Marco Fanciulli
- Department of Materials Science, University of Milano - Bicocca, Italy
| | - Moamen Jbara
- Schulich Faculty of Chemistry, Technion - Israel Institute of Technology, Haifa 3200003, Israel
| | - Aharon Blank
- Schulich Faculty of Chemistry, Technion - Israel Institute of Technology, Haifa 3200003, Israel.
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7
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Chu A, Schlecker B, Kern M, Goodsell J, Angerhofer A, Lips K, Anders J. On the modeling of amplitude-sensitive electron spin resonance (ESR) detection using voltage-controlled oscillator (VCO)-based ESR-on-a-chip detectors. MAGNETIC RESONANCE (GOTTINGEN, GERMANY) 2021; 2:699-713. [PMID: 37905224 PMCID: PMC10539732 DOI: 10.5194/mr-2-699-2021] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/05/2021] [Accepted: 08/17/2021] [Indexed: 11/02/2023]
Abstract
In this paper, we present an in-depth analysis of a voltage-controlled oscillator (VCO)-based sensing method for electron spin resonance (ESR) spectroscopy, which greatly simplifies the experimental setup compared to conventional detection schemes. In contrast to our previous oscillator-based ESR detectors, where the ESR signal was encoded in the oscillation frequency, in the amplitude-sensitive method, the ESR signal is sensed as a change of the oscillation amplitude of the VCO. Therefore, using VCO architecture with a built-in amplitude demodulation scheme, the experimental setup reduces to a single permanent magnet in combination with a few inexpensive electronic components. We present a theoretical analysis of the achievable limit of detection, which uses perturbation-theory-based VCO modeling for the signal and applies a stochastic averaging approach to obtain a closed-form expression for the noise floor. Additionally, the paper also introduces a numerical model suitable for simulating oscillator-based ESR experiments in a conventional circuit simulator environment. This model can be used to optimize sensor performance early on in the design phase. Finally, all presented models are verified against measured results from a prototype VCO operating at 14 GHz inside a 0.5 T magnetic field.
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Affiliation(s)
- Anh Chu
- Institute of Smart Sensors, University of Stuttgart, Pfaffenwaldring 47, 70569 Stuttgart, Germany
| | - Benedikt Schlecker
- Institute of Smart Sensors, University of Stuttgart, Pfaffenwaldring 47, 70569 Stuttgart, Germany
| | - Michal Kern
- Institute of Smart Sensors, University of Stuttgart, Pfaffenwaldring 47, 70569 Stuttgart, Germany
| | - Justin L. Goodsell
- Department of Chemistry, University of Florida, Gainesville, FL32611-7200, USA
| | | | - Klaus Lips
- Department Spins in Energy Materials and Quantum Information Science (ASPIN), Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin, Germany
| | - Jens Anders
- Institute of Smart Sensors and IQST (Center for Integrated Quantum Science and Technology), University of Stuttgart, Pfaffenwaldring 47, 70569 Stuttgart, Germany
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Abhyankar N, Agrawal A, Shrestha P, Maier R, McMichael RD, Campbell J, Szalai V. Scalable microresonators for room-temperature detection of electron spin resonance from dilute, sub-nanoliter volume solids. SCIENCE ADVANCES 2020; 6:6/44/eabb0620. [PMID: 33115735 PMCID: PMC7608791 DOI: 10.1126/sciadv.abb0620] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/27/2020] [Accepted: 09/14/2020] [Indexed: 06/11/2023]
Abstract
We report a microresonator platform that allows room temperature detection of electron spins in volumes on the order of 100 pl, and demonstrate its utility to study low levels of dopants in perovskite oxides. We exploit the toroidal moment in a planar anapole, using a single unit of an anapole metamaterial architecture to produce a microwave resonance exhibiting a spatially confined magnetic field hotspot and simultaneously high quality-factor (Q-factor). To demonstrate the broad implementability of this design and its scalability to higher frequencies, we deploy the microresonators in a commercial electron paramagnetic resonance (EPR) spectrometer operating at 10 GHz and a NIST-built EPR spectrometer operating at 35 GHz. We report continuous-wave (CW) EPR spectra for various samples, including a dilute Mn2+-doped perovskite oxide, CaTiO3, and a transition metal complex, CuCl22H2O. The anapole microresonator presented here is expected to enable multifrequency EPR characterization of dopants and defects in perovskite oxide microcrystals and other volume-limited materials of technological importance.
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Affiliation(s)
- Nandita Abhyankar
- Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742, USA.
- National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - Amit Agrawal
- Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742, USA
- National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - Pragya Shrestha
- National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
- Theiss Research, La Jolla, CA 92037, USA
| | - Russell Maier
- National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - Robert D McMichael
- National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - Jason Campbell
- National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - Veronika Szalai
- National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
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Implantable microchip containing oxygen-sensing paramagnetic crystals for long-term, repeated, and multisite in vivo oximetry. Biomed Microdevices 2019; 21:71. [PMID: 31286244 DOI: 10.1007/s10544-019-0421-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
EPR oximetry is established as a viable method for measuring the tissue oxygen level (partial pressure of oxygen, pO2) in animal models; however, it has not yet been established for measurements in humans. EPR oximetry requires an oxygen-sensing paramagnetic probe (molecular or particulate) to be placed at the site/organ of measurement, which may pose logistical and safety concerns, including invasiveness of the probe-placement procedure as well as lack of temporal stability and sensitivity for long-term (repeated) measurements, and possible toxicity in the short- and long-term. In the past, we have developed an implantable oxygen-sensing probe, called OxyChip, which we have successfully established for oximetry in pre-clinical animal models (Hou et al. Biomed. Microdevices 20, 29, 2018). Currently, OxyChip is being evaluated in a limited clinical trial in cancer patients. A major limitation of OxyChip is that it is a large (1.4 mm3) implant and hence not suitable for measuring oxygen heterogeneity that may be present in solid tumors, chronic wounds, etc. In this report, we describe the development of a substantially smaller version of OxyChip (0.07 mm3 or 70 cubic micron), called mChip, that can be placed in the tissue of interest using a 23G syringe-needle with minimal invasiveness. Using in vitro and in vivo models, we have shown that the microchip provides adequate EPR sensitivity, stability, and biocompatibility and thus enables robust, repeated, and simultaneous measurement from multiple implants providing mean and median pO2 values in the implanted region. The mChips will be particularly useful for those applications that require repeated measurements of mean/median pO2 in superficial tissues and malignancies.
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