Measurement of Magnetic Nanoparticles by Small HTS SQUID Array

We propose a method to investigate the brain activity of a small animal by measuring blood flow with magnetic nanoparticles (MNPs) using a high-Tc Superconducting Quantum Interference Device (SQUID) array. For the preliminary study, we fabricated a three channel high-Tc SQUID array and demonstrated the detection of a small volume of water diluted MNPs in motion. Two detection methods were applied; one was dc field measurement and the other was dc with ac field measurement. In the latter case, a second harmonic response of the nonlinear M-H characteristics of MNPs was detected. In the dc magnetic field measurement, it was demonstrated that the signal from each SQUID magnetometer was dependent on its position and the movement of the MNP sample. The detectable minimum iron content was compared between the dc and dc with ac field measurement. As a result, it was found that the minimal detectable iron content by ac with dc measurement was 12.2 ng with an SNR of 2.3 and was 1/2 times smaller than that detected by the DC field measurement.