A multi-frequency magnetic particle spectroscopy system for systematic characterization and highly sensitive detection of magnetic nanoparticles

Systematic characterization and highly sensitive detection of magnetic nanoparticles (MNPs) is of great importance to investigate the magnetic properties of the MNPs for biomedical applications. In this study, a multi-frequency magnetic particle spectroscopy (MPS) system is developed to measure the magnetic response of the MNPs in different ac magnetic fields. A model for the description of the output signal of the MPS system is deduced to analyze the signal-to-noise ratio of the MNP harmonics. The noise source, including the Gaussian noise and harmonic distortion from the excitation magnetic field, is quantitatively measured and comprehensively analyzed to investigate their influences on the limit-of-detection (LOD) of the MPS system. The MPS signal and dynamic magnetization curve of the MNPs are measured in different ac magnetic fields with the developed MPS system. In addition, a series of MNP samples with different iron concentrations are prepared for experiments to determine the LOD, indicating an LOD of 2.3 ng in terms of iron. The dependence of the LOD on the Gaussian noise and the harmonic distortion is discussed. The present work indicates that one needs to comprehensively consider the influence factors of the Gaussian noise and harmonic distortion to develop a sensitive MPS system with multi-frequency excitation.