In this paper, we propose and demonstrate a Brownian relaxation-based mixing-frequency method to test sample viscosities. This method uses excitatory and detection coils and Brownian relaxation-dominated superparamagnetic nanoparticles, which are sensitive to the characteristics of the liquid environment such as viscosity. Oscillating magnetic fields can induce harmonics through the nonlinear magnetization curve of superparamagnetic nanoparticles. Phase lag of the third-harmonic signal and the induced voltage ratio of the fifth over the third harmonic signals are collected. We build up standard graphs by plotting collected data from eight magnetic nanoparticle (MNP) mixtures with different viscosities. For any unknown liquids mixed with MNPs, we can collect phase lag and voltage ratio information and insert these data into the aforementioned standard graphs. This in vitro viscosity test can be done in 1 min. Our experimental result showed a 0.3% error rate for the liquid viscosity test.
- Brownian relaxation
- Superparamagnetic nanoparticles