Concurrent quantification of magnetic nanoparticles temperature and relaxation time

Abstract

Purpose The harmonic spectrum of the magnetization of magnetic nanoparticles (MNPs) in the presence of an applied magnetic field can be used to characterize the properties of the microenvironment of the MNPs. The change in temperature and relaxation time has been measured by varying the magnetic field amplitudes or frequency to obtain the harmonic spectrum. However, scaling estimates of temperature or relaxation time are poor if both change simultaneously. In this work, we show that scaling over both the amplitude and frequency of the applied magnetic field allows both the temperature and relaxation to be estimated simultaneously. Methods The scaling methods previously used to measure temperature and relaxation times individually have been expanded to two dimensions allowing both parameters to be estimated simultaneously. Samples with different temperature and relaxation times were measured using a magnetic nanoparticle spectrometer to verify this two‐dimensional scaling method. Simulations were also carried out for a range of nanoparticle sizes, and the best particle sizes were estimated for this two‐dimensional method. Results The two‐dimensional scaling method achieved a mean error of 0.83% for relaxation time by considering the temperature variation as well as relaxation time changes. The temperature and viscosity of the MNPs were measured simultaneously with the mean error of 1.03°C and 0.011 mPas. For monodisperse particles with Brownian relaxation, simulation showed that core radius of 16 nm and hydrodynamic radius of 23 nm had best accuracy for the scaling method. Conclusions The two‐dimensional scaling method allows both temperature and relaxation time to be estimated simultaneously. The measurement accuracy can be improved by combining information in ratios and phases of the magnetic harmonics of the magnetization and by choosing the optimal particle sizes.

Investigation of Commercial Iron Oxide Nanoparticles: Structural and Magnetic Property Characterization

“…For homogeneous bioassays that are based on a conjugation-mediated change in Brownian relaxation time, MNPs should be thermally blocked. ,− Thus, an in-depth study on the Brownian and Néel relaxation times of these MNPs under different driving fields should be carried out. , For magnetic hyperthermia therapy, the dissipated energy or specific absorption rate (SAR) is directly proportional to the imaginary component of AC susceptibility and saturation magnetization ( M s ) of MNPs, the applied field frequency, and the amplitude squared. − Thus, a high M s of MNPs does not guarantee a high SAR, and practical measurements on the hyperthermia performance are required to find out which SHA series MNPs are better suited for hyperthermia applications.…”

Magnetic nanoparticles and magnetic particle spectroscopy-based bioassays: a 15 year recap

“…Other applications of MPS platforms in clinical theragnostic are worth a mention, such as blood clot formation monitoring [224,225], mechanical force monitoring [301], detection of cold-chain breaches [302], the temperature, pH, and viscosity measurements [254,257,303], the MNP characterization [36,241], the in situ MNP biodegradation monitoring [304], etc. For example, Khurshid et al proposed to use MPS platform for a noninvasive evaluation of thrombus maturity, providing the promise of much earlier and more accurate diagnosis of diseases ranging from stroke to myocardial infarction to deep vein thrombosis, as shown in figure 12(B) [224,225].…”

Quantification of magnetic nanoparticles by compensating for multiple environment changes simultaneously

“…The dimensionless variables give scaling relationships between relaxation time and applied magnetic field frequency and between temperature and applied magnetic field amplitude. This allows the estimation of relaxation time and temperature change 11 . The harmonics are directly proportional to the number of NPs present after correcting the changes in relaxation time and in temperature.…”