We applied prepolarization field and high-$T_c$ superconducting quantum interference device (SQUID) detector to enhance nuclear magnetic resonance signal in a microtesla magnetic field. The minimum measuring magnetic field is $8.9\mu \mathrm{T}$ at which the proton resonance frequency is $380\mathrm{Hz}$ . The specificity instrumentation and the difficulty of using a high-$T_c$ SQUID with prepolarization field were investigated. We applied gradient field to perform one-dimensional proton imaging in a microtesla magnetic field. Additionally, low field high-$T_c$ SQUID-based NMR systems are promising in biomagnetic research due to its use, for example, in imaging with hyperpolarized noble gas.

Via immunomagnetic reduction assay, bio-molecules can be quantitatively detected with the aid of bio-functionalized magnetic nanoparticles, which are used as labeling markers for specific bio-molecules. To achieve an ultra-high sensitivity in the detection of bio-molecules, the superconducting quantum interference device (SQUID) looks very promising as a sensor for the magnetic signal that are related to the concentration of the detected bio-molecules. We had developed a single channel SQUID-based magnetosusceptometer, but for increasing the detection through-put, we have developed a multi-channel SQUID-based magnetosusceptometer. In this work, the design and the working principle of a 4-channel SQUID-based magnetosusceptometer are introduced. By utilizing scanning technology, 4 samples can be logged into a SQUID-based magnetosusceptometer simultaneously. Be noted that only one single SQUID magnetometer has been used in the magnetosusceptometer. The precision and the sensitivity of detecting bio-molecules by using a 4-channel SQUID-based magnetosusceptometer have been investigated. The detected bio-molecules are biomarkers for Alzheimer's disease.

The characterization of cancerous livers in rats using nuclear magnetic resonance and magnetic resonance imaging (NMR/MRI) based on high-${\text{T}}_{\text{c}}$ superconducting quantum interference devices (SQUIDs) is presented. The $\text{T}_1{}^{-1}$ were observed to be $6.5\pm 0.5{\text{s}}^{-1}$ for controlled livers and $2.85\pm 0.2{\text{s}}^{-1}$ for cancerous livers, which indicate that the ${\text{T}}_1$ can be used to distinguish the cancerous tissues from controlled liver tissues. The intensity ratio for tap water, cancerous tissue, and controlled tissue, respectively, is 1:1.15:0.56 at ${\text{T}}_{\text{Bp}}=1\text{s}$ . The SQUID-detected NMR/MRI exhibits potential applications in research and clinics.

Due to their ultrahigh sensitivity to magnetic flux, superconducting quantum interference devices (SQUIDs) are able to detect biomagnetic signals. By labeling biotargets with magnetic nanoparticles, several groups have shown that SQUIDs are promising as quantitative probes of biotargets by measuring their magnetic properties. In this work, we describe the design and construction of a high-transition-temperature radio-frequency SQUID magnetometer system for measuring the magnetic relaxation of labeled avidin. We also describe the synthesis of magnetic nanoparticles coated with biotin for use in labeling the avidin. Furthermore, the specifications of the SQUID-based magnetically labeled immunoassay of avidin are explored.