Application of magnetic field over-modulation for improved EPR linewidth measurements using probes with Lorentzian lineshape

Abstract

Magnetic field modulation in CW electron paramagnetic resonance (EPR) is used for signal detection. However, it can also distort signal lineshape. In experiments where the linewidth information is of particular importance, small modulation amplitude is usually used to limit the lineshape distortion. The use of small modulation amplitude, however, results in low signal-to-noise ratio and therefore affects the precision of linewidth measurements. Recently, a new spectral simulation model has been developed enabling accurate fitting of modulation-broadened EPR spectra in liquids. Since the use of large modulation amplitude (over-modulation) can significantly enhance the EPR signal, the precision of linewidth measurements is therefore greatly improved. We investigated the overmodulation technique in EPR oximetry experiments using the oxygen-sensing probe lithium octan-butoxy-substitued naphthalocyanine (LiNc-BuO). Modulation amplitudes 2-18 times the intrinsic linewidth of the probe were applied to increase the spectral signal-to-noise ratio. The intrinsic linewidth of the probe at different oxygen concentrations was accurately extracted through curve fitting from the enhanced spectra. Thus, we demonstrated that the over-modulation model is also applicable to particulate oxygen-sensing probes such as LiNc-BuO and that the lineshape broadening induced by oxygen is separable from that induced by over-modulation. Therefore, the overmodulation technique can be used to enhance sensitivity and improve linewidth measurements for EPR oximetry with particulate oxygensensing probes with Lorentzian lineshape. It should be particularly useful for in vivo oxygen measurements, in which direct linewidth measurements may not be feasible due to inadequate signal-to-noise ratio.

Digital detection and processing of multiple quadrature harmonics for EPR spectroscopy

“…Figure 5 compares the performance of a quadrature receiver with that of a single-channel receiver, for varying values of φ 0 . For a single-channel receiver, a complex Lorentzian signal model [31] was used to estimate τ , while for a quadrature receiver the proposed IPRE was used for the estimation.…”

Enabling Sensor Technologies for the Quantitative Evaluation of Engineered Tissue

“…Significant techniques are devised to improve EPR line width measurements by the application of magnetic field over-modulation and by twostep deblurring. 20,23,76 A limitation of the EPROM technology is the generation of line width maps restricted to a 2D map as shown in Fig. 8.…”

Multisite EPR oximetry from multiple quadrature harmonics

“…Recent efforts to accelerate EPR data collection include both hardware and algorithm developments. For example, overmodulation [10], fast scan [11], rapid scan [12], pulsed EPR [13], parametric modeling [14], adaptive and uniform data sampling [15], digital detection [16, 17, 18] and multisite oximetry [19, 20] have shown potential to accelerate the acquisition process.…”