high-Tc Superconducting Quantum Interference Research Articles

Investigation of Inkjet Printed Composites Based on Single-Walled Carbon Nanotubes With Superparamagnetic Nanoparticles

Porous-matrix composites comprising single-walled carbon nanotubes (SWCNTs) with bound magnetic nanoparticles (NPs) as filler are interesting multifunctional materials whose electrical and magnetic parameters can be used as hallmarks for identification of a genuine document or a bank note, for example. We have formulated stable functional ink based on commercially available product composed of SWCNTs (76 wt. %) and iron-based NPs (11 wt. %) and deposited them on four different thin sheet materials at a given dosage with the use of specialized inkjet printer. To study the magnetic properties, a high-Tc superconducting quantum interference device (HTS SQUID) was designed and fabricated. The printed samples were magnetized in the weak dc magnetic field (3.0 mT/μ0) and moved in the direction of applied field in close proximity to a SQUID sensor. It was found that peak-to-peak stray magnetic field of a magnetized sample (being proportional to its average magnetization) depends on the type of sheet material on which the ink was printed. The larger is the thickness of the printed layer comprising SWCNTs with magnetic NPs, the lower is the signal. Since iron-based NPs are superparamagnetic due to their small size (mean size ~ 4 nm), the difference in the magnetization may result from the difference in the contribution of exchange interaction between NPs. The performed calculations demonstrated that the decay length of electron wave function characteristic of the magnetization is about seven times larger than that of the hopping conductivity in the composites, thus suggesting the mechanism of indirect exchange interaction between NPs involving SWCNTs.

High-Tc superconducting detector for highly-sensitive microwave magnetometry

We have fabricated arrays of High-Tc Superconducting Quantum Interference Devices (SQUIDs) with randomly distributed loop sizes as sensitive detectors for Radio Frequency (RF) waves. These subwavelength size devices known as Superconducting Quantum Interference Filters (SQIFs) detect the magnetic component of the electromagnetic field. We used a scalable ion irradiation technique to pattern the circuits and engineer the Josephson junctions needed to make SQUIDs. Here, we report on a 300 SQUID series array with the loop area ranging from 6 to 60 μm2, folded in a meander line covering a 3.5 mm × 120 μm substrate area, made out of a 150 nm thick YBa2Cu3O7 film. Operating at a temperature of T = 66 K in an unshielded magnetic environment under low DC bias current (I = 60 μA) and a DC magnetic field (B = 3 μT), this SQIF can detect a magnetic field of a few picoteslas at a frequency of 1.125 GHz, which corresponds to a sensitivity of a few hundreds of fT/Hz and shows a linear response over 7 decades in RF power. This work is a promising approach for the realization of low dissipative subwavelength gigahertz magnetometers.

Static and radio frequency magnetic response of high Tc superconducting quantum interference filters made by ion irradiation

Superconducting quantum interference filters (SQIF) are promising devices for radio frequency (RF) detection combining low noise, high sensitivity, large dynamic range and wide-band capabilities. Impressive progress has been made recently in the field, with SQIF based antennas and amplifiers showing interesting properties in the GHz range using the well-established Nb/AlOx technology. The possibility to extend these results to high temperature superconductors (HTS) is still open, and different techniques to fabricate HTS SQIFs compete to make RF devices. We report on the DC and RF response of a high temperature SQIF fabricated by the ion irradiation technique. It is made up of 1000 superconducting quantum interference devices in series, with loop areas randomly distributed between 6 and 60 μm2. The DC transfer factor is ∼450 V T−1 at optimal bias and temperature, and the maximum voltage swing ∼2.5 mV. We show that such a SQIF detects RF signals up to 150 MHz. It presents linear characteristics for RF power spanning more than five decades, and non-linearities develop beyond PRF = −35 dBm in our set-up configuration. The second harmonic generation has been shown to be at a minimum at the functioning point in the whole range of frequencies. A model has been developed which captures the essential features of the SQIF RF response.

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.

Volume-amplified magnetic bioassay integrated with microfluidic sample handling and high-Tc SQUID magnetic readout.

A bioassay based on a high-Tc superconducting quantum interference device (SQUID) reading out functionalized magnetic nanoparticles (fMNPs) in a prototype microfluidic platform is presented. The target molecule recognition is based on volume amplification using padlock-probe-ligation followed by rolling circle amplification (RCA). The MNPs are functionalized with single-stranded oligonucleotides, which give a specific binding of the MNPs to the large RCA coil product, resulting in a large change in the amplitude of the imaginary part of the ac magnetic susceptibility. The RCA products from amplification of synthetic Vibrio cholera target DNA were investigated using our SQUID ac susceptibility system in microfluidic channel with an equivalent sample volume of 3 μl. From extrapolation of the linear dependence of the SQUID signal versus concentration of the RCA coils, it is found that the projected limit of detection for our system is about 1.0 × 105 RCA coils (0.2 × 10−18 mol), which is equivalent to 66 fM in the 3 μl sample volume. This ultra-high magnetic sensitivity and integration with microfluidic sample handling are critical steps towards magnetic bioassays for rapid detection of DNA and RNA targets at the point of care.

Harmonics distribution of iron oxide nanoparticles solutions under diamagnetic background

The static and dynamic magnetizations of low concentrated multi-core iron oxide nanoparticles solutions were investigated by a specially developed high-Tc Superconducting Quantum Interference Device (SQUID) magnetometer. The size distribution of iron oxide cores was determined from static magnetization curves concerning different concentrations. The simulated harmonics distribution was compared to the experimental results. Effect of the diamagnetic background from carrier liquid to harmonics distribution was investigated with respect to different intensity and position of peaks in the magnetic moment distribution using a numerical simulation. It was found that the diamagnetic background from carrier liquid of iron oxide nanoparticles affected the harmonics distribution as their concentration decreased and depending on their magnetic moment distribution. The first harmonic component was susceptible to the diamagnetic contribution of carrier liquid when the concentration was lower than 24 μg/ml. The second and third harmonics were affected when the peak position of magnetic moment distribution was smaller than m = 10−19 Am2 and the concentration was 10 ng/ml. A highly sensitive detection up to sub-nanogram of iron oxide nanoparticles in solutions can be achieved by utilizing second and third harmonic components.

Operation of a high-TC SQUID gradiometer with a two-stage MEMS-based Joule–Thomson micro-cooler

Practical applications of high-TC superconducting quantum interference devices (SQUIDs) require cheap, simple in operation, and cryogen-free cooling. Mechanical cryo-coolers are generally not suitable for operation with SQUIDs due to their inherent magnetic and vibrational noise. In this work, we utilized a commercial Joule–Thomson microfluidic two-stage cooling system with base temperature of 75 K. We achieved successful operation of a bicrystal high-TC SQUID gradiometer in shielded magnetic environment. The micro-cooler head contains neither moving nor magnetic parts, and thus does not affect magnetic flux noise of the SQUID even at low frequencies. Our results demonstrate that such a microfluidic cooling system is a promising technology for cooling of high-TC SQUIDs in practical applications such as magnetic bioassays.

High-Tc superconducting quantum interference filters (SQIFs) made by ion irradiation

Superconducting quantum interference filters (SQIFs) are arrays of superconducting loops of different sizes including Josephson junctions (JJ). For a random distribution of sizes, they present a non-periodic response to an applied magnetic field, with a large transfer function and a magnetic field sensitivity potentially improved with respect to that of a single SQUID. Such properties make SQIFs interesting devices to detect the magnetic component of electromagnetic waves at microwave frequencies. We have used the highly scalable technique of ion irradiation to make SQUIDs and SQIFs based on commercial YBa2Cu3O7 films, and studied their properties. Both display optimal performance as a function of temperature and bias current, that can be understood in the frame of numerical simulations that we developed. The role of asymmetries and dispersion in JJ characteristics (routinely found in high Tc superconductors technologies) is also studied. We have found that none of them impede the existence of a SQIF effect but both play a role on the emergence of the optimal point. We finally present results on SQIF made with 2000 SQUIDs in series, showing a transfer function .

Determining the time-dependent effective relaxation time of biofunctionalized magnetic nanoparticles conjugated with biotargets by using a high-Tc SQUID-based ac susceptometer for a magnetic immunoassay

In this study, we determined the time-dependent effective relaxation time (τeff) of biofunctionalized magnetic nanoparticles (BMNs) that were conjugated with biotargets for magnetic immunoassays. The BMNs were anti-alphafetoprotein (AFP)-coated onto dextran-coated magnetic nanoparticles to yield Fe3O4–anti-AFP. The biotarget was AFP. The time-dependent phase delay θ(t) of magnetization relative to the applied field strength was determined using a homemade high-Tc superconducting quantum interference device-based ac susceptometer. The detected θ(t) was then analyzed to derive τeff(t), the results of which showed that τeff(t) increased over time. Additionally, the change in τeff after the BMNs conjugated with the AFP (Δτeff) increased with the AFP concentration (ΦAFP). We attribute this to the additional magnetization generated when the BMNs conjugated with the AFP, which thereby reduced the Néel and Brownian relaxations and consequently improved the τeff. We established the relationship between ΔτAFP and ΦAFP and thus provide a foundation for assaying unknown quantities of AFP.

Effect of diamagnetic contribution of water on harmonics distribution in a dilute solution of iron oxide nanoparticles measured using high-Tc SQUID magnetometer

The magnetization curve of iron oxide nanoparticles in low-concentration solutions was investigated by a highly sensitive high-Tc superconducting quantum interference device (SQUID) magnetometer. The diamagnetic contribution of water that was used as the carrier liquid was observed in the measured magnetization curves in the high magnetic field region over 100mT. The effect of the diamagnetic contribution of water on the generation of harmonics during the application of AC and DC magnetic fields was simulated on the basis of measured magnetization curves. Although the diamagnetic effect depends on concentration, a linear relation was observed between the detected harmonics and concentration in the simulated and measured results. The simulation results suggested that improvement could be expected in harmonics generation because of the diamagnetic effect when the iron concentration was lower than 72μg/ml. The use of second harmonics with an appropriate bias of the DC magnetic field could be utilized for realization of a fast and highly sensitive detection of magnetic nanoparticles in a low-concentration solution.

Imaging of Magnetic Nanoparticles Using a Second Harmonic of Magnetization With DC Bias Field

We have developed a method to improve the detection sensitivity for the magnetization ${M}$ of magnetic nanoparticles (MNPs) using a high Tc superconducting quantum interference device magnetometer. The ${M}$ response of MNP to an applied magnetic field ${H}$ ( ${M}$ – ${H}$ characteristics) can be divided into a linear region and a saturation region, which are separated at a transition point ${H}_{k}$ . When applying an excitation ac magnetic field ( ${H}_{\rm ac}$ ) and an additional dc bias field ${H}_{\rm dc} {=} {H}_{k}$ , the second harmonic of M reaches a maximum due to the nonlinearity of its ${M}$ – ${H}$ characteristics. This harmonic is stronger than any other harmonics, including a third harmonic. The advantage of using the second harmonic response is that the response can be measured even in a small field ${H}_{\rm ac}$ . The ${M}$ response of MNP was systematically analyzed and experimentally demonstrated. For conventional detection using a third harmonic, the amplitude of the ${H}_{\rm ac}$ must be larger than the threshold level, which is almost the same as ${H}_{k}$ . Detection methods using a second harmonic can be applied to magnetic particle imaging. We finally demonstrate the construction of a 1-D image of two separated bottle-shaped MNP samples using the method with a lock-in amplifier.

Magnetic Coupling between SQUID and Probe of STM-SQUID

An STM-SQUID microscope has been developed by combining a scanning tunneling microscope (STM) and a high-Tc superconducting quantum interference device (SQUID) to simultaneously observe the surface morphology and the local magnetic field. In our microscope, a permalloy probe with high permeability, whose tip is electrochemically polished, is placed between the rf-SQUID and the sample. The probe plays a flux guide role of transferring the local magnetic field of the sample to the SQUID. The probe tip could be approached as close to the sample surface as possible within a few nm by an STM feedback control. The SQUID detects the magnetic field from the end of probe. It is also important to bring the probe end close to the SQUID. In this paper, we have investigated the magnetic coupling between the SQUID and the probe in the STM-SQUID microscope setup by decreasing the gap distance between the SQUID and the end of probe from 4.5mm to 0.1mm. The magnetic signal detected by the SQUID was increased as the distance between the SQUID and the probe was decreased. As the result, the magnetic images of a nickel thin film sample became clearer with decreasing the distance.

Ultra-Sensitive Contaminant Detection System Using High-Tc SQUID

We report the fabrication of magnetic metallic contaminant detectors using multiple high-Tc superconducting quantum interference devices (SQUIDs) for food. Finding small metallic contaminants is important for food safety. People may ingest contaminants that are accidentally mixed in with the food. Hence, a detection method of small contaminants in food is required. Given the lower detection limit for practical X-ray usage is in the order of 1 mm, a detection system using a SQUID is a more powerful tool for sensitive inspections. We design and set up a three-channel high-Tc rf-SQUID inspection system for food. We report the successful detection of a small φ0.3-mm steel particle for the food detection system.

Visualization of ion transportation in an electrolyte using an HTS-SQUID gradiometer

Direct detection of magnetic fields generated by the ion currents in electrolytic cells was performed and the ion currents were mapped during a cyclic voltammetry experiment. A high-Tc superconducting quantum interference device (SQUID) gradiometer with ramp-edge Josephson junctions was used as the detector and thus the first derivative of the magnetic field along the electrolytic cell surface was obtained. The electric potential vs. the reference electrode was measured between −0.3V and 0.8V and the hysteresis signals caused by the redox reactions of the electrolyte were observed. The vector component of the ion current during cyclic voltammetry was mapped along the electrolytic cell. As a demonstration of visualization of ion transportation, the magnetic signal was also measured at various positions above the electrolytic cell surface.

Optimization of the detection coil of high-Tc superconducting quantum interference device-based nuclear magnetic resonance for discriminating a minimum amount of liver tumor of rats in microtesla fields

This study presents an optimization of the detection coil of high-Tc superconducting quantum interference device (SQUID)-based nuclear magnetic resonance (NMR) in microtesla fields for discriminating a minimum amount of liver tumor in rats by characterizing the longitudinal relaxation rate, T1−1, of tested samples. The detection coil, which was coupled to the SQUID through a flux transformer, was optimized by varying the copper wires’ winding turns and diameters. When comparing the measured NMR signals, we found that the simulated NMR signal agrees with simulated signals. When discriminating liver tumors in rats, the averaged longitudinal relaxation rate was observed to be T1−1 = 3.3 s−1 for cancerous liver tissue and T1−1 = 6.6 s−1 for normal liver tissue. The results suggest that it can be used to successfully discriminate cancerous liver tissue from normal liver tissues in rats. The minimum amount of samples that can be detected is 0.2 g for liver tumor and 0.4 g for normal liver tissue in 100 μT fields. The specimen was not damaged; it can be used for other pathological analyses. The proposed method provides more possibilities for examining undersized specimens.

Battery-Powered Wireless Flux-Locked Loop Circuit for Operating High-Tc SQUID

A battery-operated wireless flux-locked-loop (FLL) circuit for operating a high-Tc superconducting quantum interference device (SQUID) was developed and tested. This wireless battery-type FLL circuit consists of an FLL unit and a PC interface. A local area network with the TCP-IP protocol for wireless mode was used for communication between the PC interface and a controlling PC. The battery unit can power the FLL circuits for four hours. The FLL circuit had two bias modes: ac and dc. When the wireless-battery-type FLL circuit was implemented in a SQUID, the system noise generated by a wireless network became intrinsic high-Tc SQUID noise. Also, a 1/f noise was reduced in the case of the ac-bias-current mode. Consequently, the wireless-battery-type FLL circuit can operate a high-Tc SQUID with high sensitivity.

Study on signal intensity of low field nuclear magnetic resonance via an indirect coupling measurement

We carry out an ultra-low-field nuclear magnetic resonance (NMR) experiment based on high-Tc superconducting quantum interference devices (SQUIDs). The measurement field is in a micro-tesla range (∼10 μT−100 μT) and the experiment is conducted in a home-made magnetically-shielded-room (MSR). The measurements are performed by the indirect coupling method in which the signal of nuclei precession is indirectly coupled to the SQUID through a tuned copper coil transformer. In such an arrangement, the interferences of applied measurement and polarization field to the SQUID sensor are avoided and the performance of the SQUID is not destroyed. In order to compare the detection sensitivity obtained by using the SQUID with that achieved using a conventional low-noise-amplifier, we perform the measurements using a commercial room temperature amplifier. The results show that in a wide frequency range (∼1 kHz−10 kHz) the measurements with the SQUID sensor exhibit a higher signal-to-noise ratio. Further, we discuss the dependence of NMR peak magnitude on measurement frequency. We attribute the reduction of the peak magnitude at high frequency to the increased field inhomogeneity as the measurement field increases. This is verified by compensating the field gradient using three sets of gradient coils.

Relaxation of biofunctionalized magnetic nanoparticles in ultra-low magnetic fields

In this work, the spin-spin relaxation rate, 1/T2, and spin-lattice relaxation rate, 1/T1, of protons’ spins induced by biofunctionalized magnetic nanoparticles and ferrofluids are investigated using a high-Tc superconducting quantum interference device-detected magnetometer in ultra-low fields. The biofunctionalized magnetic nanoparticles are the anti-human C-reactive protein (antiCRP) coated onto dextran-coated superparamagnetic iron oxides Fe3O4, which is labeled as Fe3O4-antiCRP. The ferrofluids are dextran-coated iron oxides. It was found that both 1/T2 and 1/T1 of protons in Fe3O4-antiCRP are enhanced by the presence of magnetic nanoparticles. Additionally, both the 1/T1 and 1/T2 of Fe3O4-antiCRP are close to that of ferrofluids, which are dextran-coated Fe3O4 dispersed in phosphate buffer saline. Characterizing the relaxation of Fe3O4-antiCRP can be useful for biomedical applications.

Characterizing the field-dependent T1-relaxation and imaging of ferrofluids using high-Tc superconducting quantum interference device magnetometer in low magnetic fields

In this paper, we investigate the field-dependent T1-relaxation and T1-contrast imaging of ferrofluids using high-Tc superconducting quantum interference device (SQUID)-detected nuclear magnetic resonance and imaging in low magnetic fields, where T1 is the spin-lattice relaxation time. It was found that the 1/T1 of ferrofluids increases when the prepolarization field increases. We attribute this to the enhanced magnetic-field gradients generated from the induced magnetization that accelerates the T1-relaxation more in a high strength of fields in comparison to a low strength of fields. Using phantoms with different relaxation times, the T1-contrast images are demonstrated in low magnetic fields, which can be promising for discriminating tumors.

Discriminating hepatocellular carcinoma in rats using a high-Tc SQUID detected nuclear resonance spectrometer in a magnetic shielding box.

In this study, we report the spin-lattice relaxation rate of hepatocellular carcinoma (HCC) and normal liver tissue in rats using a high-Tc superconducting quantum interference device (SQUID) based nuclear magnetic resonance (NMR) spectrometer. The resonance spectrometer used for discriminating liver tumors in rats via the difference in longitudinal relaxation time in low magnetic fields was set up in a compact and portable magnetic shielding box. The frequency-domain NMR signals of HCC tissues and normal liver tissues were analyzed to study their respective longitudinal relaxation rate T1 −1. The T1 −1 of liver tissues for ten normal rats and ten cancerous rats were investigated respectively. The averaged T1 −1 value of normal liver tissue was (6.41±0.66) s−1, and the averaged T1 −1 value of cancerous tissue was (3.38±0.15) s−1. The ratio of T1 −1 for normal liver tissues and cancerous liver tissues of the rats investigated is estimated to be 1.9. Since this significant statistical difference, the T1 −1 value can be used to distinguish the HCC tissues from normal liver tissues. This method of examining liver and tumor tissues has the advantages of being convenient, easy to operate, and stable.