A Multi-frequency Magnetic Particle Spectroscopy System for the Characterization of Magnetic Nanoparticles

Magnetic particle spectroscopy (MPS) is one of the most versatile methods to characterize the magnetic properties of magnetic nanoparticles (MNPs). The excitation magnetic field is one of the most crucial factors that affects the MPS signal of the MNPs. In this study, a multi-frequency MPS system is developed to investigate the MPS signal of MNPs in different ac magnetic fields. The MPS system consists of a multi-channel excitation module for the generation of different-frequency ac magnetic fields and a detection module for the measurement of the magnetic response of the MNPs. The MPS system allows to generate ac magnetic fields with a frequency up to 32.6 kHz and amplitude up to 25 mT. The MPS signals of the MNPs in different ac magnetic fields are measured to systematically evaluate the performance of the multi-frequency MPS system, including the MNP spectra and its dynamic magnetization curve. In addition, the signal-to-noise ratio (SNR) of the MPS system is quantitively assessed with measured MPS signals of a given MNP sample and DI water. Furthermore, a series of MNP samples with different iron concentrations are prepared and measured to evaluate the limit-of-detection (LOD) in terms of iron concentration. The influence of the excitation magnetic field, including frequency and amplitude, is discussed based on the SNRs of the measured harmonics. Experimental results show that the LOD is 2.3 ng in terms of iron.