Iron Speciation in Animal Tissues Using AC Magnetic Susceptibility Measurements: Quantification of Magnetic Nanoparticles, Ferritin, and Other Iron-Containing Species

Abstract

The simultaneous detection and quantification of several iron-containing species in biological matrices is a challenging issue. Especially in the frame of studies using magnetic nanoparticles for biomedical applications, no gold-standard technique has been described yet and combinations of different techniques are generally used. In this work, AC magnetic susceptibility measurements are used to analyze different organs from an animal model that received a single intratumor administration of magnetic nanoparticles. The protocol used for the quantification of iron associated with the magnetic nanoparticles is carefully described, including the description of the preparation of several calibration standard samples of nanoparticle suspensions with different degrees of dipolar interactions. The details for the quantitative analysis of other endogenous iron-containing species such as ferritin or hemoglobin are also described. Among the advantages of this technique are that tissue sample preparation is minimal and that large amounts of tissue can be characterized each time (up to hundreds of milligrams). In addition, the very high specificity of the magnetic measurements allows for tracking of the nanoparticle transformations. Furthermore, the high sensitivity of the instrumentation results in very low limits of detection for some of the iron-containing species. Therefore, the presented technique is an extremely valuable tool to track iron oxide magnetic nanoparticles in samples of biological origin.

Influence of Magnetic Nanoparticle Degradation in the Frame of Magnetic Hyperthermia and Photothermal Treatments

“…When plotted per mass of sample, the height of the out-ofphase susceptibility maxima acts as a surrogate measurement of the amount of iron in the form of particles in a given sample. 28 In the degradation experiment, a reduction of the out-of-phase susceptibility maxima height along time was observed for both samples. In agreement with the TEM observation, the observed results indicated the decrease of the amount of particles present in the sample as a consequence of the degradation processes.…”

“…In the AC magnetic susceptibility measurements, in all cases, the typical maxima in both the in-phase and out-of-phase susceptibility components, which serve as a fingerprint of the presence of MNPs in complex matrices, were observed. 28 The temperature locations of such maxima, being at slightly lower temperatures for the out-of-phase component in comparison with the in-phase one, were indicative of a magnetic relaxation process. 29 Therefore, in order to focus on the temperature locations of the susceptibility maxima along the degradation process, the results were scaled to their maxima (Figure 4A).…”

“…When plotted per mass of sample, the height of the out-of-phase susceptibility maxima acts as a surrogate measurement of the amount of iron in the form of particles in a given sample . In the degradation experiment, a reduction of the out-of-phase susceptibility maxima height along time was observed for both samples.…”

“…As discussed before, magnetic susceptibility measurements were selected as an adequate characterization technique, given their capacity to analyze large portions of animal tissues (even complete organs in the case of mice), to track changes in particle size and amount, and to distinguish MNPs from endogenous iron-containing species. ,, NPs@PMAO particles were intratumorally administered to a xenograft mouse model bearing a pancreatic tumor in one flank. Animals were sacrificed at different time points after the MNP administration and tumor tissues were collected and analyzed magnetically.…”

Different coatings on magnetic nanoparticles dictate their degradation kinetics in vivo for 15 months after intravenous administration in mice

“…The cotton samples were then placed inside a standard capsule for magnetic measurements and hysteresis loops with a maximum field of 5 T were measured in a Vibrating Sample Magnetometer (MLVSM9, MagLab 9 T, Oxford Instruments, UK). In addition, to prepare samples with different degree of dipolar interactions [ 43 ] the particles were diluted in hot agar (1% w/v) and allowed to cool down to RT in an ultrasound bath [ 44 ]. Solid agar solutions were then freeze-dried and placed into gelatin capsules for magnetic characterization using a QuantumDesign MPMS-XL SQUID magnetometer.…”