Comparison of Electron Spin Resonance Spectroscopy and Inductively-Coupled Plasma Optical Emission Spectroscopy for Biodistribution Analysis of Iron-Oxide Nanoparticles

Abstract

Magnetic nanoparticles (MNP) have been widely studied for use in targeted drug delivery. Analysis of MNP biodistribution is essential to evaluating the success of targeting strategies and the potential for off-target toxicity. This work compared the applicability of inductively-coupled plasma optical emission spectroscopy (ICP-OES) and electron spin resonance (ESR) spectroscopy in assessing MNP biodistribution. Biodistribution was evaluated in 9L-glioma bearing rats administered with MNP (12-25 mg Fe/kg) under magnetic targeting. Ex vivo analysis of MNP in animal tissues was performed with both ICP-OES and ESR. A cryogenic method was developed to overcome the technical hurdle of loading tissue samples into ESR tubes. Comparison of results from the ICP-OES and ESR measurements revealed two distinct relationships for organs accumulating high or low levels of MNP. In organs with high MNP accumulation such as liver and spleen, data were strongly correlated (r = 0.97, 0.94 for liver and spleen, respectively), thus validating equivalency of the two methods in this high concentration range (> 1000 nmol Fe/g tissue). The two sets of measurements, however, differed significantly in organs with lower levels of MNP accumulation such as brain, kidney, and the tumor. Whereas ESR resolved MNP to 10-55 nmol Fe/g tissue, ICP-OES failed to detect MNP due to masking by endogenous iron. These findings suggest that ESR coupled to cryogenic sample handling is more robust than ICP-OES, attaining better sensitivity in analyses. Such advantages render ESR the method of choice for accurate profiling of MNP biodistribution across tissues with high variability in nanoparticle accumulation.

Degradation of magnetic nanoparticles mimicking lysosomal conditions followed by AC susceptibility

“…One of the biggest problems faced in the characterization of magnetic nanoparticles in tissues arises from the fact that most particles used for biomedical applications are based on iron oxides, and there is a large amount of endogenous iron already in the tissues. Thus, the distinction between the iron from the particles and endogenous iron present in the tissue is a complicated task [6]. Techniques that exploit the specific magnetic properties of the particles and, therefore, discern them from tissue iron-containing species are currently being used to analyze magnetic nanoparticles in tissue samples, in particular electron spin resonance (ESR) [6], ferromagnetic resonance [12], field-dependent magnetization [28], or alternating current (AC) magnetic susceptibility [16] measurements.…”

“…Thus, the distinction between the iron from the particles and endogenous iron present in the tissue is a complicated task [6]. Techniques that exploit the specific magnetic properties of the particles and, therefore, discern them from tissue iron-containing species are currently being used to analyze magnetic nanoparticles in tissue samples, in particular electron spin resonance (ESR) [6], ferromagnetic resonance [12], field-dependent magnetization [28], or alternating current (AC) magnetic susceptibility [16] measurements. In the latter case, the temperature dependence of the AC magnetic susceptibility has been proven to be a powerful tool for the quantitative analysis of magnetic nanoparticles and biogenic species in animal tissue samples, as it allows the study of the particle biodistribution and degradation processes [27].…”

Biodistribution and Pharmacokinetic Studies of SPION Using Particle Electron Paramagnetic Resonance, MRI and ICP-MS

“…Applicability of such instrumentation ranges from the laboratory analytical activity to the clinical environment. Previous work [17] has shown the advantages of the electron spin resonance (ESR) spectroscopy compared with inductively coupled plasma optical emission spectroscopy (e.g., ESR can distinguish between endogenous and exogenous sources of iron, ESR shows greater sensitivity for MNPs than for endogenous iron species but only in a biodistribution study of SPIONs). As opposed to pEPR method which results in a direct measurement of the SPIONs not requiring further data analysis, the ESR data were deduced from absorption ESR spectra, this is the first derivative of absorbed microwave power with respect to the applied field, from which the double integral was calculated to obtain a number proportional to the resonating electronic spins in the sample.…”

“…As opposed to pEPR method which results in a direct measurement of the SPIONs not requiring further data analysis, the ESR data were deduced from absorption ESR spectra, this is the first derivative of absorbed microwave power with respect to the applied field, from which the double integral was calculated to obtain a number proportional to the resonating electronic spins in the sample. Moreover a limitation imposed by the sample preparation for these ESR measurements is the necessity to section the tissue samples in to 2 mm 3 cubes to fit in the thin ESR glass tubes, in addition samples have to be precooled to prevent preparation errors due to tissue loss or cross contamination [17]. By contrast, pEPR is performed at low magnetic fields (10 millitesla) and low RF frequencies (300 MHz), offering the advantage that a much larger sample volume can be inserted and measured at room temperature.…”

The effect of mechanical properties of iron oxide nanoparticle-loaded functional nano-carrier on tumor targeting and imaging

“…The amounts of IONP were calculated from a standard calibration curve of ICP-AES. To get a standard calibration curve, the amounts of endogenous iron in each organ without IONP were subtracted because animal tissues have rich iron-containing proteins such as hemoglobin, transferrin and ferritin [31]. Therefore, the amounts of IOPN were calculated considering the different background iron levels in each organ.…”