Kyushu University · Engineering
Professor Keiji Enpuku's research lab specializes in the development and application of high-temperature superconducting quantum interference devices (SQUIDs) for ultra-sensitive magnetic field detection. The lab focuses on advancing biomagnetic sensing technologies, particularly in the context of medical diagnostics using magnetic nanoparticles as labels for antigen-antibody reactions. Key research directions include optimizing SQUID performance under thermal noise, enhancing signal-to-noise ratios through innovative circuit designs, and applying these technologies to real-world biomedical assays. The lab also investigates the fundamental physics of SQUID behavior, especially in the context of high-Tc superconductors operating at liquid nitrogen temperatures.
Figures are computed from collected data and may differ slightly.
A system is developed to magnetically measure biological antigen-antibody reactions with a superconducting quantum interference device (SQUID) magnetometer. In this system, antibodies are labeled with magnetic nanoparticles of γ-Fe 2 O 3 , and the antigen-antibody reactions are measured by detecting the magnetic field from the magnetic nanoparticles. A setup of the system is described, and the sensitivity of the system is studied in terms of detectable weight of nanoparticles. Magnetic particles
Effects of thermal noise on the characteristics of the dc superconducting quantum interference device (SQUID) have been studied. Numerical simulation on the SQUID characteristics operating at T=77 K has been performed by taking into account the thermal noise. It is shown that the voltage versus flux relation of the dc SQUID is degraded considerably with the thermal noise. The degradation becomes significant when the inductance of the SQUID increases. Due to this degradation, there exists signifi
Globally, the demand for improved health care delivery while managing escalating costs is a major challenge. Measuring the biomagnetic fields that emanate from the human brain already impacts the treatment of epilepsy, brain tumours and other brain disorders. This roadmap explores how superconducting technologies are poised to impact health care. Biomagnetism is the study of magnetic fields of biological origin. Biomagnetic fields are typically very weak, often in the femtotesla range, making th
Comprehensive comparison between theory and experiment has been made on the characteristics of a high-Tc dc superconducting quantum interference device (SQUID). Using the theoretical expressions for the SQUID characteristics, we can quantitatively predict the transfer function Vφ and the magnetic-flux noise SΦ from SQUID parameters without any adjustable parameter. It is shown that the theoretical predictions agree well with the experimental results for a wide range of SQUID parameters. This agr
The effect of a damping resistance on the relation between a voltage V and a magnetic flux Φ of a dc SQUID is studied theoretically for the case with a large SQUID parameter βL=2LI0/Φ0 , where L is a loop inductance, I0 is a critical current, and Φ0 is the flux quantum. An approximate analytical expression for the V-Φ relation is obtained by replacing the Josephson junctions with ac current generators. It is shown that the V-Φ relation becomes almost independent of the value of βL in the case of
A high T/sub c/ SQUID system is developed for the application to biological immunoassay. In this application, magnetic nanoparticles are used as magnetic markers to perform immunoassay, i.e., to detect binding reaction between an antigen and its antibody. Design and set up of the system is described. Minimum detectable amplitude of the magnetic flux is 0.6 m/spl Phi//sub 0/ for the measurement bandwidth from 0.2 Hz to 5 Hz when we use a magnetometer. The system noise does not increase when the m
Magnetic biosensing techniques that are based on the use of bio-functionalized magnetic nanoparticles (magnetic markers) and superconducting quantum interference devices (SQUIDs) are expected to have various advantages when compared with conventional biosensing methods. In this paper, we review the recent progress made in magnetic biosensing techniques. First, we describe the most important parameters of magnetic markers that are intended for use in biosensing, i.e., the magnetic signal and the
ac susceptibility measurement of magnetic markers in solution was performed for the liquid phase detection of biological targets. First, the properties of the magnetic markers were clarified, such as size distribution, frequency dependence of susceptibility, and field dependence of magnetization. Next, we demonstrated a detection method in which we used large polymer beads to immobilize and prolong the Brownian relaxation time of the bound markers. In this method, we could detect the bound marke
High T/sub c/ SQUID system is developed for the detection of the biological binding-reaction between antigen and its antibody. In this measurement, the antibody is labeled with magnetic nanoparticles, and the magnetic signal from the nanoparticles is measured. The excitation field of a few mT is applied in parallel to the SQUID in order to magnetize the nanoparticles. Due to mechanical misalignment, however, the vertical component of the excitation field couples to the SQUID, and degrades the sy
Detection of the biological binding-reaction between an antigen andits antibody was performed by using a magnetic marker and a high Tc superconducting quantum interference device (SQUID) magnetometer. In this method, the binding reaction is detected by measuring the magnetic field from the marker. A new marker made of Fe3O4 particle with diameter of 25 nm was developed, and the remanent field of the marker was used for the detection of the antigen called Interleukin 8 (IL8). It was shown that th
In order to study the effect of a multiturn input coil on superconducting quantum interference device (SQUID) characteristics, the radio frequency (rf) properties of the coupling circuit between the SQUID coil and the input coil are studied. For the measurement of rf properties of the coupling circuit, the so-called expanded model of the coupling circuit using normal metals was adopted, which is shown to be very useful for this purpose. It is shown that the SQUID coil cannot be expressed by a si
A complete circuit model of a dc superconducting quantum interference device (SQUID) coupled to a multiturn input coil has been developed. With this model, it is shown that the rf properties of the coupled SQUID can be calculated using only the given parameters of the SQUID. There are no adjustable parameters. The resonant structures in the SQUID characteristics caused by the presence of the input coil have been quantitatively studied. Methods to suppress the resonant structures have also been i
The ac susceptibility of magnetic markers in solution was studied for biosensor application, where the marker consisted of magnetic nanoparticles and a coating material. From the frequency dependence of the susceptibility caused by the Brownian rotation of the marker, we estimated the distribution of marker size, which is an important parameter for biosensor application. For this purpose, we analyzed the experimental data by the singular value decomposition (SVD) method. Using this method, we ca
Magnetic immunoassays utilizing magnetic markers and a high-T/sub c/ SQUID have been performed. We first showed a design of the SQUID for the sensitive detection of the magnetic signal from the marker, where the spatial distribution of the signal field was taken into account. Using the design, we can obtain the relationship between the magnetization of the maker and the signal flux detected with the SQUID. This relationship is important for quantitative evaluation of the immunoassay. Next, we de
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