Advances in rapid scan EPR spectroscopy

Abstract

Progress has been made in hardware for low frequencies, demonstrations of rapid frequency scans, hybrid instrumentation, and improved deconvolution software. The recent availability of the commercial Bruker BioSpin rapid scan accessory for their X-band EMX and Elexsys systems makes this technique available to a wide range of users without the need to construct their own system. Developments at lower frequencies are underway in several labs with the goal of facilitating in vivo and preclinical rapid scan imaging. Development of new deconvolution algorithms will make data processing more robust. Frequency scans have substantial promise at higher frequencies. New examples of applications show the wide applicability and advantages of rapid scan.

Keywords: Electron paramagnetic resonance; In vivo EPR; Resolution of hyperfine splittings; Signal-to-noise.

Figure 1.

Comparison of signal detection by CW and rapid-scan EPR.

Figure 2.

Compact electromagnetic designed by rapid scan imaging of mice at frequencies between 700 MHz and 1 GHz. Reproduced with permission from Buchanan et al. (Buchanan et al. 2018a).

Figure 3.

Rapid scan spectra of LiPc recorded with 2 MHz modulation frequency (107,000 THZ/s at the center of the spectrum) at 3 magnetic fields. Dashed lines correspond to the spectra calculated using the modified Bloch equations. Reproduced with permission from O. Laguta et al (2018) (Laguta et al. 2018).

Figure 4.

Overlays of expanded segments of CW (blue) and rapid-scam spectra (orange) showing the agreement in lineshapes and improved signal-to-noise for the same data acquisition times. A) CTPO, B) DPNO, C) galvinoxyl and D) perylene. Reproduced with permission from McPeak et al (2020) (McPeak et al. 2020).

Figure 5.

Sagittal slices and histograms of the dinitroxide cleavage rate k^obs in FSa tumor (A) before and (B) 24 hr after application of BSO. Magneta outline shows the tumor border as obtained from a co-registered MRI image. The histograms shows k^obs in all voxels of the tumor. Sagittal slices and histograms of the clearance rate k^clr in FSs tumor (C) before and (D) after application of BSO. The histogram shows k^clr in all voxels of the tumor. Reproduced with permission from Epel et al (2017) (Epel et al. 2017).

Figure 6.

Rapid scan (left) and CW (right) spectra of α-hydrogenated silicon samples, after baseline subtraction, obtained with the data acquisition time, T_acq. The plot includes the raw data (black), data after applying a low-pass filter (blue), and simulations obtained with EasySpin (red). Reproduced with permission from Möser et al (2017) (Möser et al. 2017).

Figure 7.

First-derivatives of rapid-scan spectra of 0.2 mM CTPO in ethanol obtained with a sample height of 3 mm, scan width of 60 G and 20 mG B₁. A) Triangular scan with frequency of 1.8 kHz and scan rate of 220 G/s. B) Sinusoidal scan with frequency of 1.8 kHz and scan rate in the center of the spectrum of 350 kG/s. C) Sinusoidal scan with frequency of 6.2 kHz and scan rate in the center of the spectrum of 1200 kG/s. D) Sinusoidal scan with frequency of 10.5 kHz and scan rate in the center of the spectrum of 2000 kG/s. Reproduced with permission from McPeak et al (2020) (McPeak et al. 2020).

Figure 8.

Saturation curves for rapid scan (red circles) and CW (black triangles) EPR on a sample of α-hydrogenated silicon. Signal intensities are plotted as a function of the microwave magnetic field, B₁. Intensity values are normalized such that the slope in the linear regime (black dashed line) is equal for RS and CW. Circles mark the B₁ that was selected to acquiring data. The inset magnifies the low-power regime for the CW experiments. Reproduced with permission from Möser et al (2017) (Möser et al. 2017).