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Highlights • Procedure for magnetic parameters evaluation of magnetic nanoparticles is presented. • Suspended sample M-H curve, immobilized sample M-H curve and AC susceptibility are used. • Parameters of Resovist MNP sample and its two fractionated samples were evaluated. • Resovist sample parameters were given by volume-weighted average of the two fractionated samples. Abstract We present a procedure for the comprehensive evaluation of parameters of magnetic nanoparticles (MNPs), such as saturation magnetization, core-size distribution, anisotropy energy constant, and characteristic time for Néel relaxation for use in biomedical applications and fundamental MNPs research. The static magnetization curve of suspended and immobilized MNP samples and the AC susceptibility of immobilized samples were used for the evaluation of these parameters. The magnetic properties reconstructed from the obtained parameters agreed with the experimental results, indicating the accuracy of the estimation procedure. Using the procedure, the parameters of the commercial Resovist MNP sample were evaluated. Then, the Resovist sample was magnetically fractionated into two MNP samples with large and small core sizes, and the parameters of the two fractionated samples were evaluated. It was demonstrated that the parameters of the Resovist sample are given by the volume-weighted average for those of the fractionated samples. [ABSTRACT FROM AUTHOR]

• Studied the effect of viscosity on amplitude and phase of harmonic signals from magnetic nanoparticles. • Viscosity dependences are related to co-existence of Néel and Brownian relaxation. • Viscosity dependences are discussed in terms of field dependent relaxation time of MNP. • Investigated frequency dependence of the viscosity effect on harmonic signals. • Discussed viscosity dependence of different parameters used for MNP thermometry. We studied effect of viscosity on harmonic signals of magnetic nanoparticles (MNP). Harmonic signals are measured when an excitation field with amplitude (~3 mT) and frequency (~10 kHz) is applied, where the relaxation mechanism of the used MNP is affected by the coexistence of Brownian and Néel processes. Viscosity dependence of amplitude and phase of fundamental, third and fifth harmonics are measured when viscosity changed from 0.89 mPa·s to 12.6 mPa·s. The measured viscosity dependences are discussed in terms of field dependent relaxation time of MNP. We also discuss a method to determine temperature and viscosity from the measured harmonic signals. [ABSTRACT FROM AUTHOR]

• Studied the effect of viscosity on the harmonic signals from magnetic nanoparticles. • First harmonic decreased with increase in viscosity while third and fifth increased. • First and third harmonics had negative correlation, whereas the third and fifth had positive correlation. • Viscosity dependences are related to co-existence of Néel and Brownian relaxation. • Proposed a method for estimation of viscosity and temperature of MNP samples. We studied the effect of viscosity on the harmonic signals of magnetic nanoparticles (MNPs) for thermometry application. Although thermometry is based on the temperature dependence of MNPs harmonic signals, they are also affected by the viscosity of the surrounding media. Therefore, we first perform numerical calculation to qualitatively show the effect of viscosity on the first (M 1), third (M 3) and fifth (M 5) harmonic signals when an excitation field with medium amplitude (3 mT) and high frequency (10 kHz) is applied. We then present the experimental results for Resovist MNPs samples when viscosity is changed from 0.89 to 5.2 mPa·s. We obtained qualitative agreement between numerical calculation and experimental results on the viscosity dependences. Next, we study the correlation between the changes in harmonic signals caused by viscosity variation. The M 1 and M 3 had negative correlation in their change, while M 3 and M 5 had positive correlation. Due to the positive correlation, the ratio M 5 / M 3 became almost independent of viscosity when appropriate amplitude and frequency were chosen for the excitation field. We also proposed a method to accurately estimate both viscosity and temperature of the MNPs sample from the measured harmonic signals even when the viscosity is not known in advance, which will be useful for precise thermometry. [ABSTRACT FROM AUTHOR]

• We showed wash-free detection of C-reactive proteins based on the Brownian relaxation of magnetic markers. • Brownian relaxation time was prolonged by using cluster formation of bound markers. • Two types of magnetic properties, i.e., third-harmonic signal and magnetic relaxation, were used for the measurement. • We also discussed the relationship between the signals that was measured with the two measurement methods. We demonstrate the wash-free detection of biological targets based on the Brownian relaxation of magnetic markers. The Brownian relaxation time of bound markers was prolonged by using a cluster (or agglomerate) of bound markers that was formed via the binding reaction between markers and targets. Thus, bound and free markers were differentiated magnetically by using the difference in their relaxation times. Two types of magnetic properties, i.e., third-harmonic signal and magnetic relaxation, were used for measurement. The concentration of target was detected from the decrease in the third-harmonic signal and the increase in the magnetic-relaxation signal. We demonstrated the detection of C-reactive proteins using these two properties. In both cases, a good correlation was obtained between the measured signal and the concentration of target. It was also shown that the two methods had different concentration dependences, which will be caused mainly by the distribution of cluster size of the bound markers. [ABSTRACT FROM AUTHOR]