Keywords:SQUID, magnetometer, magnetic nanoparticles
Many types of magnetic measurement systems using superconducting devices, such as low-temperature (LTS) and high-temperature (HTS) superconducting quantum interference devices (SQUIDs) and superconducting pickup coils, have been developed. Highly sensitive magnetometers that detect the weak magnetic characteristics of biological materials using HTS-SQUID have been developed for other clinical and biological applications. The hybrid-type magnetometer performs three functions: VSM, relaxation measurement, and third-harmonic signal analysis. Aqueous mixtures of ethanol as solvent have been investigated. By analyzing the magnetization curves of magnetic nanoparticles (MNPs), one obtains the magnetic moment distributions of the nanoparticles. A liquid-phase immunoassay method is able to detect the third-harmonic signals of MNPs by an HTS magnetometer.