Rapid Viscosity Measurement Using Arbitrary Frequency Magnetic Particle Spectrometer

Magnetic particle spectrometer (MPS) is the device for characterizing the properties of magnetic nanoparticle (MNP) suspensions, such as viscosity, temperature, and concentration. Specifically, in viscosity measurement, MPS usually works at one or several fixed frequencies. It is challenging to find the appropriate frequency for viscosity measurement of different MNP suspensions. The frequency parameter can be introduced into the measurement method to improve the measurement accuracy. Here, we developed an arbitrary frequency MPS to measure the harmonic amplitudes of the magnetization signals of MNPs, which were generated at various frequencies. A method of measuring the viscosity of MNP suspensions by harmonic ratios at different frequencies was proposed. The viscosity measurement time used in the experiment is 1 s, and the shortest measurement time available is 0.2 s. Experimental results show that the arbitrary frequency MPS can measure the viscosity of samples ranging from 0.77 mPa
$\cdot \text{s}$
to 3.87 mPa
$\cdot \text{s}$
, and the average measurement deviation is 2.7%. The method was validated using plasma samples from normal rabbits and high-fat diet (HFD) rabbits. Normal rabbit measurements differed from the reference by less than 4.5%, and the plasma viscosity of normal and HFD rabbits could be clearly distinguished.