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Detecting magnetic field is of great importance for many applications, such as magnetoencephalography and underground prospecting. There have been many magnetometers being widely used since the age of Hall magnetometer. One of the magnetometers, the superconducting quantum interference device, is capable of measuring femtotesla magnetic fields at cryogenic temperature. However, a solid-state magnetometer with femtotesla sensitivity under ambient conditions remains elusive. Here we present a hybrid magnetometer based on the ensemble nitrogen-vacancy centers in diamond with the sensitivity of ( 195 ± 60 ) fT / Hz 1 / 2 under ambient conditions, which can be further advanced to 11 fT / Hz 1 / 2 at 100 Hz with cutting-edge fabrication technologies. Our method will find potential applications in biomagnetism and geomagnetism.

The superconducting quantum interference device (SQUID) is a highly sensitive detector for magnetic flux or any quantity that can be efficiently converted into flux. This chapter provides a short introduction into the basic function of a SQUID, its operation, and its design for magnetic field and current sensing. It shows by several examples that the device is very versatile and important for a variety of applications such as biomagnetism, astronomy, low-temperature physics, and metrology. The chapter measures with the commercial variant of the electronics and include the noise contribution from the preamplifier and shows the noise spectra as examples. The dc SQUID is dominant in the field of Nbbased sensors, and the rf SQUID is practically obsolete. The dc SQUID is based on two effects: flux quantization and superconducting tunneling. The chapter presents equations for calculating the inductance and the effective field-sensitive area of two representative superconducting structures.

With a growing number of applications utilizing THz radiation appearing on the market the question of health protection against non-ionizing electromagnetic fields arises in this frequency range, as at lower frequencies before. To date, about 50 independent empirical studies on living organisms, model systems and cells have been performed to clarify bio-electromagnetic interaction in the THz frequency range. Many of these studies find behavioral effects or effects on the cellular level, even at non-thermal exposure levels, while others do not report effects other than thermally induced damage. We discuss the general challenges in performing reliable field exposure experiments in the THz frequency range and describe a methodology that was adopted in a large campaign searching for genotoxic effects of THz radiation in vitro.

In this work an alternative neuroscience tool for electromagnetic measurements of neurons at the level of individual cells is developed. To perform such measurements we propose the integration of an array of magnetoresistive sensors on micro-machined Si probes capable of being inserted within the brain without further damage. Si-etch based micromachining process for neural probes is demonstrated in the manufacture of a probe with 15 magnetoresistive sensors in the tip of each shaft. Magnetic tunnel junction sensors with dimensions of 30 μm × 2 μm, sensitivities of 3.32 V/T and detectivity of ≈13 nT/Sqrt (Hz) are placed in the end of the sharply defined probe tips. In order to measure the small signals coming from the neurons, a homemade signal amplifying system was used with a noise level of 240 n V RMS for the system bandwidth. The full system noise is 2772 n V RMS., This work was supported in part by FCT projects NanoSciEra/0002/2008, PTDC/EEA-ELC/108555/2008 and PTDC/CTM-NAN/110793/2009. J Amaral thanks FCT for grant SFRH/BD/45488/2008. INL acknowledges partial funding from the ON2 project from PO-Norte. INESC-MN acknowledges FCT funding through the Instituto de Nanociência e Nanotecnologia (IN) Associated Laboratory

Superparamagnetic beads are increasingly used in biomedical assays to manipulate, transport, and maneuver biomaterials. We present a low-cost integrated system designed in bulk CMOS to manipulate and separate biomedical magnetic beads. The system consists of 8 × 8 coil-arrays suitable for single bead manipulation, or collaborative multi-bead manipulation, using pseudo-parallel executions. We demonstrate the flexibility of the design in terms of different coil sizes, DC current levels, and layout techniques. In one array module example, the size of a single coil is 30 μm × 30 μm and the full array occupies an area of 248 μm × 248 μm in 0.5 μm CMOS technology. The programmable DC current source supports 8 discrete levels up to 1.5 mA. The total power consumption of the entire module is 9 mW when running at full power.

We review the development of low parasitic capacitance sub-micrometer cross-type Josephson tunnel junctions for their use in highly sensitive and field-stable SQUID magnetometers. The potential of such junctions is shown on I – V characteristics as well as on Fraunhofer diffraction patterns. The evaluation of Fiske steps lead to a specific junction capacitance of about 62 fF/μm 2 for a critical current density of about 1.7 kA/cm 2 . The avoidance of any idle-region – the undesired overlap between superconducting electrodes around the junction – due to a self-aligned junction definition process lead to highly sensitive SQUIDs; multiloop SQUID magnetometers exhibiting exceptionally low magnetic field noise levels as low as 0.3 fT/Hz 1/2 , as well as large usable voltage swings of more than 150 μVpp. Furthermore, junction dimensions in the sub-micrometer range allowed for very high tolerable background fields during cool-down of up to 6.5 mT. In operation mode, the SQUID magnetometers recovered completely from magnetization pulses of up to 76 mT. With respect to their easy and reliable usage as well as their high sensitivity, the presented SQUID sensors are adequate for many applications, like in geophysics, biomagnetism or low-field magnetic resonance imaging.

We have developed sensitive micro magnetic sensors referred to as MI sensors based on magneto-impedance effect in amorphous wires and CMOS IC electronic circuits providing a sharp-pulse excitation. Micro sized MI-HIC chips have been in mass production of electronic compasses by Aichi Steel Corp. since 2002 for mobile phones and since 2010 for smart phones. Recently we have realized pico-Tesla (10-8 Oe) resolution for micro MI sensors making use of ultralow intrinsic magnetic noise in amorphous wires with the pulse magnetoimpedance effect. The pico-Tesla MI sensor is useful especially for bio-magnetic measurements without any magnetic shielding at room temperature. In order to avoid a risk of traffic accident due to noise reduction electric vehicles, an alert system for the pedestrians having a smart phone would be useful, if pico-Tesla MI sensor were built in the smart phones.

A system to evaluate nanoparticles efficiency in hyperthermia applications is presented. The method allows a direct measurement of the power dissipated by the nanoparticles through the determination of the first harmonic component of the in quadrature magnetic moment induced by the applied field. The magnetic moment is measured by using an induction method. To avoid errors and reduce the noise signal a double in phase demodulation technique is used. To test the system viability we have measured nanowires, nanoparticles and copper samples of different volumes to prove by comparing experimental and modeled results.

When coupled to a giant magnetoresistive (GMR) sensor, a superconducting loop containing a constriction can be a very sensitive magnetometer. It has thermal noise levels of few fT/sqrt(Hz), comparable to low-Tc SQUID noise, with a flat frequency response. These mixed sensors are good candidates for detection of weak biomagnetic signals, like a cardiac or neuronal signature. Furthermore, being sensitive to the flux, mixed sensors can be used for nuclear magnetic resonance (NMR) detection and Magnetic Resonance Imaging (MRI) especially at low fields. They are very robust and accept strong RF pulses with a very short recovery time compared to tuned RF coils, which allow measurements of broad signals (short relaxation time or multiple resonances). We will first present the last generation sensors having a noise level of 3 fT/sqrt(Hz) and we will show signals measured at low frequency (magnetocardiography–magnetoencephalography range) and at higher frequency (NMR signals). The use of additional flux transformers for improving the signal-to-noise will be discussed. Finally, we will present perspectives for low-field MRI, which can be combined with neural signal detection (MEG), especially for brain anatomy and temporal response on the same experimental setup.

We demonstrate the use of a magnetic tunnel junction (MTJ) sensor as a probe for non-contact scanning microscopy of magnetically labeled DNA microarrays. Induced magnetic stray fields from 2.8 mum diameter magnetic particles are detected using the MTJ sensor, while two dimensional scanning generates the magnetic map of the DNA microarray with a spatial resolution of 1 mum over a large scan area exceeding 1 cm2. Current particle-sensor spacing of ~20 mum results in a detection resolution of ~30 magnetic particles within each 100 mum diameter DNA spot. Our results highlight the use of scanning magnetoresistive microscopy as a convenient and powerful technique for the accurate detection and identification of biomolecules tagged with magnetic particles.

Recently, affinity magnetic beads have been widely used in immunomagnetic cell sorting (IMCS) technology. Today, we can easily sort and analyze DNA and antibodies (immunoglobulin) using various types of affinity magnetic beads available in the market. The diameters of these affinity magnetic beads used in immunomagnetic cell sorting are limited to above approximately 1 mum because of the low magnetic fields induced by permanent magnets. Now, nano-sized affinity magnetic beads are strongly desired to achieve high resolutions. We have been studying and attempting to develop a high-gradient magnetic separation (HGMS) system that employs a superconducting magnet to induce a considerably higher magnetic field than that induced by a permanent magnet in order to trap smaller nano-sized affinity magnetic beads by a filter made of fine stainless steel wool. In this study, we constructed a prototype of a desktop-type HGMS system using a cryocooler-cooled LTS magnet and conducted preliminary experiments on trapping the nano-sized magnetic particles. Furthermore, we investigated the magnetic field distribution and magnetic force around a magnetic wire in the filter by means of a numerical simulation.

high-Tc SQUID, magnetometer, bio-magnetism, multi-channel, rat MCG. Abstract. Three-channel directly-coupled-type high-Tc SQUID magnetometer array, with pick-up coil size of 1.5 mm2 comparable to the lift-off distance of the developed multi-channel SQUID system, was designed. In this design, two slits were introduced in the SQUID ring to improve the inductive coupling between the pick-up coil and the SQUID ring to obtain the field sensitivity of about 700 fT/Hz1/2. With the SQUID array that was mounted on the multi-channel SQUID system, the measurements of magnetocardiogram of rat were demonstrated to evaluate the system performance.

Superconducting quantum interference devices (SQUIDs) are intrinsically very sensitive detectors of magnetic flux. Flux sensitivities of one millionth of a flux quantum per root Hz (1μφ0/√Hz) may typically be realized in low-temperature superconductor (LTS) materials, while sensitivities of ∼5μφ0/√Hz may be realized in high-temperature superconductor (HTS) materials. LTS devices are typically cooled with liquid helium (4 K) while HTS devices are typically cooled with liquid nitrogen (77 K). Coupling the magnetic field into a SQUID via a flux-transformer can result in a very sensitive magnetometer with, depending on the type of superconducting material used and the effective area of the flux-coupling transformer, achievable magnetic field sensitivities ranging from fT/√Hz to pT/√Hz over typical bandwidths that span hundreds of kHz. SQUID applications include NDE, biomagnetism and magnetic microscopes.

In applications for high-Tc superconducting DC-SQUIDs such as biomagnetism, nondestructive evaluation and the relaxation of magnetic nanoparticles, it is important to maintain reliable sensor performance over an extended time period. We have designed and produced DC-SQUID gradiometers based on YBa2Cu3O7−x (YBCO) thin films which are inductively coupled to a flux transformer to achieve a higher sensitivity. The gradiometers are protected against ambient atmosphere and humidity by SiO2 and amorphous YBCO layers. The noise properties of the sensor in flip–chip configuration, especially in unshielded environments, are shown. We present a comparison of Tl2Ba2CaCu2O8+x (TBCCO) thin films on buffered sapphire or LaAlO3 substrates for the flux transformer in shielded and unshielded environments. We reach a low white field gradient noise of 72 fT cm−1 Hz−1 with the TBCCO on LaAlO3 flux transformer. The electric properties of the gradiometers (critical current IC, normal state resistance RN and the transfer function VΦ) were measured over a period of one year and do not show significant signs of degradation.

In this paper we compare the detection of magnetic microparticles by HTS SQUIDs and GMR sensors. Our prototype system uses a HTS SQUID array insulated/isolated from a nonmagnetic tube in which the sample flows at room temperature. This necessarily results in a liftoff between sensor and sample in the range of 2 mm. While HTS SQUIDs typically have an intrinsic noise sensitivity that is at least two orders of magnitude better than conventional GMR sensors (~ 1 pTradicHz for washer SQUIDs compared to ~ 100 pTradicHz for the best commercial GMRs), the dipole like response of a magnetic microparticle in flow is such that this difference in noise performance can be compensated for by the reduction in standoff (order of 0.2 mm) when using a magnetoresistive sensor. Here we detail the two different approaches, present comparative results and discuss the relative merits of each setup.

A process to surface pattern polydimethylsiloxane (PDMS) with ferromagnetic structures of varying sizes (micrometer to millimeter) and thicknesses (>70 μm) is developed. Their flexibility and magnetic reach are utilized to confer dynamic, additive properties to a variety of substrates, such as coverslips and Eppendorf tubes. It is found that these substrates can generate additional modes of magnetic droplet manipulation, and can tunably steer magnetic-cell organization.

Pulsed electric field (PEF) disinfection is a promising technology for the nonthermal disinfection of water. Magnetic pulse compressors due to their high repetition rates and lifetimes, appear to be a promising alternative to the existing pulse forming circuits used for sterilization applications. The application of these systems for the purification of water has yet to be explored. The use of the short duration electrical pulses from the magnetic pulse compressor for inactivation of spores, bacteria (Escherichia coli) and viruses in drinking water is being investigated at the University of Missouri, Columbia. The test cell designed herein allows flowing tests for pulsewidths of 130-500 ns. The coupling of the magnetic modulator with the test cell and the inactivation protocols that aim at effective inactivation under optimal conditions are discussed. A 4 log reduction was seen for (Escherichia coli) E. coli at field strengths of 110 kV/cm and 70 pps, with a total energy consumption of 40 J/cm3. A comparative study of different parameters, e.g., pulsewidth, electrode gap, frequency, and electric field, which effect the microbial inactivation are also presented

Low- T c SQUIDs are currently the only devices with a sufficiently low level of noise for magnetic field measurements in the femtotesla range. An alternative to SQUIDs is to combine a superconducting flux-to-field transformer with a high sensitivity magnetoresistive sensor. With a correct design, the excitation field can be sufficiently enhanced to be measured by a magnetoresistance (MR). We have fabricated and tested a micron-sized integrated YBCO-based mixed sensor of small size. It is comprised of a GMR stack separated from a YBCO thin film by an insulating layer. A constriction in the superconducting loop drives the induced current through a small section and therefore creates field lines large enough to be detected by the GMR down to 30 fT/Hz 1/2 , that is in the range of high- T c SQUIDs. The device characteristics at 4.2 and 77 K are shown. Experimental results are compared to the theoretical gain of the structure. Applications of this sensor are for instance in the biomagnetism area, especially for magnetoencephalography, where neural signals emitted by the brain are of the order of few fT/Hz 1/2 . Various other fields are concerned, from earth mapping to fundamental physics (vortex motion, magnetic interactions, etc.).

Advancement of the recent micro/nanotechnology stimulates the renaissance of using magnetic micro/nanoparticles embedded in tissues for the target tumor hyperthermia. However, there is a strong lack of quantitative understanding of the temperature profiles thus induced by the applied external electromagnetic (EM) field, which may impede the successful operation of this therapy. In the current study, the three-dimensional quasi-steady-state EM field and transient tissue temperature behavior induced by two planar electrodes were numerically investigated. Detailed computations indicated that nanoparticles exhibit an extraordinary highly focused heating on target tumor tissue, which is much stronger than that in the surrounding areas. This heating effect depends heavily on the properties of the magnetic nanoparticles, which may vary appreciably for different samples depending on their particle sizes and microstructures. The effect of micro/nanoparticle concentration, heating area, and the frequency and strength of the external alternating EM field were also tested. Moreover, a criterion to determine the appropriate particle concentration thermally important for medical treatment was established. Given accurate thermal and EM parameters for cancerous tissue embedded with nanoparticles, the current model could possibly be applied in the hyperthermia treatment planning and help optimize the surgical procedures.

An overview is given on different thin film preparation methods to produce YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin film Josephson devices on various substrates. Beside laser deposition and ion beam etching techniques the use of inhibit technologies for patterning is discussed for the preparation of large area superconducting structures. For the deposition of large area YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// films a heater and dry etching concept is discussed. The quality of the films is compared for all these methods to optimize the crystalline quality, the superconducting properties and the long term stability of the samples. The technology of production of high sensitive and stable Josephson devices like single junctions, dc-SQUIDs and flux transformers is important with respect to applications in nondestructive evaluation and biomagnetism.

Very low magnetic fields are detected up to now using SQUID-based devices. In the femtotesla range, only low-T/sub c/ SQUIDs have a sufficiently low level of noise to measure extremely low signals, as for instance induced fields of the neural activity of the brain, for magneto-encephalography (MEG). An alternative to SQUIDs is to combine a superconducting flux-to-field transformer with a high-sensitivity giant magnetoresistive sensor (GMR). We have fabricated and performed experiments on such an integrated YBCO-based mixed sensor. It is comprised of a GMR stack separated from a YBCO thin film by an insulating layer. The induced supercurrent in the YBCO is forced through a narrow constriction, thereby creating a local field much larger than the external field. This large local field is detected by the GMR. Effective noise levels are down to 30 fT/sqrtHz, which is in the range of high-Tc Squids. Performance of this device is shown from liquid helium temperature (4.2 K) up to liquid nitrogen temperature (77K). By replacing the GMR by a Tunneling Magneto Resistance (TMR) or a Colossal Magneto Resistance (CMR) sensor, and by adjusting the dimensions to optimize the local enhancement effect, the sensitivity should reach the subfemtotesla range at low frequency. A large number of applications could be investigated by this sensor, especially in the biomagnetism area, as well as in various other fields, from earth mapping to fundamental physics (vortex motion in superconductors, magnetic interactions...).

This paper presents a method for continuous magnetophoretic separation of red and white blood cells from whole blood based on their native magnetic properties. The microsystem separates the blood cells using a high gradient magnetic separation method without the use of additives such as magnetic tagging or inducing agents. A theoretical model of the magnetophoretic microseparator is derived and verified by comparison with finite element simulation. The microseparator is fabricated using microfabrication technology, enabling the integration of microscale magnetic flux concentrators in an aqueous microenvironment, providing strong magnetic forces, and fast separations. Experimental tests are performed using a permanent magnet to create an external magnetic flux of 0.2T, and measuring the movement of red blood cells within the microchannel of the microseparator. The experimental results correlate well with the theoretical results.

We have designed and constructed a versatile magnetic tweezer primarily for intracellular investigations. The micromanipulator uses only two coils to simultaneously magnetize to saturation micron-size superparamagnetic particles and generate high magnitude constant field gradients over cellular dimensions. The apparatus resembles a miniaturized Faraday balance, an industrial device used to measure magnetic susceptibility. The device operates in both continuous and pulse modes. Due to its compact size, the tweezers can conveniently be mounted on the stage of an inverted microscope and used for intracellular manipulations. A built-in temperature control unit maintains the sample at physiological temperatures. The operation of the tweezers was tested by moving 1.28 μm diameter magnetic beads inside macrophages with forces near 500 pN.

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 system performance. In order to solve this problem, we develop two methods. One is the use of a compensation field in the case of the flux dam, and the other is the use of a switch instead of the flux dam. We also develop a magnetic marker utilizing Fe/sub 3/O/sub 4/ nanoparticle with diameter of d=25 nm. The nanoparticle is embedded in the polymer with typical diameter of 80 nm, and COOH is attached around the surface of the polymer. The properties of the marker are discussed.

An axial HTS DC-SQUID gradiometer formed by electronic subtraction with a 10 cm baseline and a gradient resolution better than 1 fT/cm Hz at 77 K has been developed and demonstrated. The best achieved gradient resolution for the planar HTS DC-SQUID gradiometer was of about 30 fT/cm Hz for both shielded and unshielded operation. A comparison of the characteristics of the gradiometers with ones of competitive room temperature sensors like fluxgates is discussed.

Magnetophysiology is the use of a superconducting quantum interference device (SQUID) based instrument to detect neuromagnetic fields evoked by electrical stimulation of brain tissue slices. In this paper we show that a SQUID based on high temperature superconductors (HTSs) would have considerable advantages over a low Tc device in this application. We construct a model of electrical activity in a hippocampal brain slice, which enables the neuromagnetic field to be determined as a function of position and distance from the tissue. We then describe the design of HTS SQUID systems for magnetophysiology and the two styles of system we are developing. Finally we use our model to show that an existing HTS SQUID magnetometer would give a superior signal to noise ratio compared to a low Tc system for the hippocampal brain slice preparation at least.

The ability to focus spherical particles (SPPs) to a deep tumor region remains one of the major challenges in magnetic drug targeting (MDT). A number of studies have attempted to overcome this problem using fast magnetic pulses and ferromagnetic rods. However, focusing of the SPPs in the deep body organs remains unsolved using existing schemes. In this paper, we propose a novel electro-magnetic actuation scheme for pushing and focusing SPPs. The simulation results demonstrate that the newly proposed actuation scheme can focus SPPs to a target surface region, inside of a block filled with an environment that has the characteristics of blood. We then investigated the effects of the proposed focusing scheme in realistic blood vessels with a maximum length of about 10–12 cm. The results show that SPPs of 500 nm can be concentrated onto a target tumor region with up to 97.9% efficiency. The proposed electromagnetic actuation scheme can maximize the efficiency of MDT, while minimizing the side effects of drugs in other tissues.

A resonant circuit is expected to be used as a heating source for hyperthermia implants, because the circuit can be effectively heated by an applied ac magnetic field. In order to realize a less invasive delivery of the implant through a catheter or injection needle, its miniaturization down to 1 mm or less is essential. However, the heating temperature of the resonant circuit is reduced by downsizing of the size of the circuit. A ferrite core in a coil is employed in order to obtain higher induced voltage in the inductor, resulting in the higher temperature rise of the resonant circuit. The resonant circuit implant consisting of the core coil has been prepared. Its diameter is 0.9 mm and the implant can be delivered through an 18 G needle.

In a system that can perform biomagnetic measurements, the most eagerly desired features include without liquid helium, unshielded operation, and low cost. We developed a high-critical-temperature (high-Tc) superconducting quantum interference device (SQUID) system to be used for taking biomagnetic measurements. The proposed device consists of a small cryostat, high-Tc SQUID magnetometer, and analog flux-locked loop (FLL) circuit. A wide dynamic range was achieved through an analog FLL circuit that used the flux quanta counting (FQC) method. We also proved the feasibility of this high-Tc SQUID system with the help of a simple prototype. The circuit performance of the analog FLL circuit was evaluated using a high-Tc SQUID. A wide dynamic range was obtained by using the analog FLL circuit.

A fully integrated low noise superconducting quantum interference device (SQUID) in a magnetometer configuration is presented. An intrinsic high voltage responsivity as high as 500 muV/Phi0 has been obtained by introducing a resonance in the voltage - magnetic flux characteristic. This resonance is induced by an integrated superconducting coil surrounding the pick-up coil and connected to one end of the SQUID output. The SQUID magnetometer exhibits a spectral density of magnetic field noise as low as 3 fT/Hz(1/2). In order to verify the suitability of the magnetometer, measurements of bandwidth and slew rate have been performed and compared with those of the same device without the resonance and with additional positive feedback. Due to their good characteristics such devices can be employed in a large number of applications including biomagnetism.

Contactless method for manipulation of polar or polarisable micro and nanoscale particles based on the dielectrophoresis force exerted by the induced electric field in high pulsed magnetic field is presented in this study. Finite element method analysis of the magnetic and resulting induced electric fields is carried out. The structure of the magnetic field generator that was based on a controlled frequency spark gap, and the structure of the coil that was used as a load are described. Experimental data showing positive dielectrophoresis on the Jurkat T-lymphoblasts is presented. The study discusses further developments of the technique, its limitations and possible applications.

Magnetic spectroscopy allows for characterization of the magnetic susceptibility of magnetic beads across a broad frequency range. This enables differentiation and quantification of multiple beads of varying types concurrently present in the active volume of a sensor's surface. A magnetic spectrometer can be used for multi-probe tagging and identification akin to multi-color fluorescent bio-sensing. We propose a new sensing methodology to perform magnetic spectroscopy and analyze various important design parameters such as SNR and gain uniformity. We present a proof-of-concept design of a fully integrated CMOS magnetic spectrometer that can detect, quantify, and characterize magnetic materials in the 1.1 GHz to 3.3 GHz frequency range, where we demonstrate magnetic multiplexing capability using a mixture of two different kinds of magnetic beads. The sensor consumes less than 2 mW of DC power within the whole frequency range, requires no external biasing magnetic fields, is implemented in a standard CMOS process, and can be powered and operated completely from a USB interface. The magnetic spectrometer not only increases the throughput and multiplexing of biosensing experiments for a given sensor area, but also can enable additional applications, such as magnetic flow cytometry and signal-collocation assays of multiple probes.

The separation of target objects conjugated with magnetic particles is a significant application in biomedicine and clinical diagnosis. Conventional magnetophoresis-based devices use a sheath flow to pre-focus the particles into a single stream and typically operate at a low flow rate. We demonstrate in this work a high-throughput, sheathless, magnetophoretic separation of magnetic and non-magnetic beads in a groove-based channel, and also report on an interesting phenomenon where the same magnetic beads in the same microchannel, but with different setups, has a different particle tracing; a binary mixture of magnetic and non-magnetic beads in a diluted ferrofluid, is then fed into the channel. These magnetic beads are focused near the centreline of the channel by exploiting positive magnetophoresis and microvortices generated by grooves, whereas the non-magnetic beads are focused along the sidewalls of the channel by negative magnetophoresis and hydrophoresis. These magnetic and non-magnetic beads are se...

The purpose of this paper is to describe and characterize a needle type giant magnetoresistance (GMR) sensor which is used in biomedical applications. In this research we have shown the main specifications of the GMR sensor and the method of the GMR sensor's sensitivity determination. The high sensitivity of this sensor allows us to obtain more accurate estimation of low concentrations of magnetic fluid, protein, bacteria and nano-micro markers in a weak magnetic field.

We present a concept of the thermally assisted magnetic tunneling junction (MTJ)-based biosensor. The sensor consists of an MTJ, an isolation layer, and a gold coating layer right underneath a biocoating layer. During the sensing phase, a current pulse heats the top free ferromagnet of the MTJ stack above its blocking temperature. The top magnet loses its magnetization at this point. During the cool down period, the top free magnet picks up its magnetization orientation based on the external magnetic field. A vertical excitation field is applied to excite the superparamagnetic biolabels during the sensing phase. If there is no magnetic biolabel captured by the sensing cell, the magnetization in MTJ top free magnetic layer will be programmed by the fringe field from the bottom pinned magnet and will be anti-parallel to the latter. If there are one or more magnetic labels captured by the sensing cell, the superparamagnetic nanoparticle(s) will generate fringe field. The top magnet follows the orientation of the in-plane fringe field component, which is parallel to the pinned bottom magnet. The sensing result can be read out by measuring the tunneling resistance of the MTJ cell. The proposed biosensor design can achieve high sensitivity in three different ways: 1) the magnetic sensing and electronic read-out operations are decoupled in time domain; 2) the binary readout increases the signal to noise ratio significantly; and 3) thermally assisted magnetic sensing decouples the sensor sensitivity from the magnetic stiffness of the sensing layer. Our simulation results demonstrate sensitivity sufficient for single nanoparticle detection. The thermal analysis indicates that the temperature on the top surface of gold layer can be maintained below 50 degC in order to avoid damage to the biocoating layer.

Integrated magnetometers based on superconducting quantum interference devices (SQUIDs) are employed for the very sensitive measurement of magnetic flux and magnetic flux density. Today, most superconducting magnetometers made from high-temperature superconductors (HTS) are based on YB a2 Cu 3 O 7 and are optimized for a temperature of 77 K. Depending on the application, the size of the magnetometers is restricted. Many applications in the non-destructive evaluation (NDE) of materials allow the use of large chips with up to 5 cm diameter. The need for integrated, multilayer magnetometers arises, when high sensitivity has to be combined with high spatial resolution with areas below 1 cm 2 . This applies to the sensors in multichannel systems for biomagnetism which have to be adapted to the size of the sources of magnetic signals in the human heart or brain. Here, a survey on the current status of integrated, thin-film YB a2 Cu 3 O 7 magnetometers is given.

Reduction for 1/f noise (or random telegraph noise) is a crucial issue for small magnetic sensors which is strongly related to structural properties and magnetic configuration. We show how it is possible to eliminate magnetic noise at low frequency in GMR/TMR sensors by a combination of cross anisotropies, window frame shapes and suitably designed magnetoresisitive stack. These sensors are superior to almost all existing field and flux sensors. Results are presented on a mixed sensor, where a superconducting loop acts as a flux-to-field transformer to the GMR sensor. This device is suitable for detection of biomagnetic signals, such as in magnetocardiography or in magnetoencephalography. Measurements on niobium-based and YBCO-based sensors are presented, leading to sensitivity of 30 fT/√Hz at 77 K for small samples. Sensitivity lower than 1 fT/√(Hz) is expected with appropriate design and use of TMR or CMR layers, which makes these a powerful alternative to SQUIDs.

We present recent work on developing a wide-field magnetic imaging system using the nitrogen-vacancy (NV) color center in diamond. The NV centers can function as a robust and bio-compatible magnetic sensor at room temperature. Optical detection of the spin state of NV centers allows magnetic field imaging with sub-micron spatial resolution. We use this imaging system to study biomagnetism. Techniques to further improve the magnetic field sensitivity and the spatial resolution are also discussed.

Over the last decade, Giant Magnetoimpedance (GMI) sensors have been intensively studied as a new possibility for measuring ultra-weak magnetic fields. Pursuing the measurement of biomagnetic fields, this paper presents a newly developed method that allows the achievement of about a hundredfold enhancement in the impedance phase sensitivity of GMI sensors and, consequently, increases the sensitivity of phase-based GMI magnetometers. Also, the electronic circuit implemented to realize the proposed method is presented and discussed, and the obtained experimental results are shown.

For many SQUID applications such as biomagnetism or non-destructive evaluation it is convenient or even necessary to work without the restrictions of a magnetically shielded room. This contribution deals with two sensors appropriate for this purpose. In the first concept we present a flip chip arrangement of a single-layer flux transformer and a single-layer SQUID, taking advantage of a simple technology. The SQUID was prepared on a bicrystal and located in the common line of two-parallel-loop arrangements. The flipped antenna was designed as a two-parallel-loop gradiometer with 26 mm baseline on a single-crystal substrate. A field gradient sensitivity of was obtained. We could demonstrate a field gradient resolution of at 1 kHz in an unshielded environment. In the second concept we integrated both the flux antenna and the SQUID on a bicrystal. The tighter coupling scheme results in smaller devices for similar field gradient sensitivities. The integrated SQUID is designed as a device on a bicrystal substrate. The remaining space is used for test structures and SQUIDs without antennae, in order to control the technology as well as the SQUID design. Parallel processed dummy substrates were used to monitor the quality of film growth by x-ray analysis. The quality of our SQUID design will be discussed on the basis of the measured field gradient sensitivity and noise. The reliability of the devices is demonstrated by an NDE type measurement.

A multi-channel high temperature superconducting interference device (high Tc SQUID) system has been developed. Step edge junctions were employed as weakly coupled Josephson junctions for the SQUID. The magnetic field resolution was 70 to 250fT/Hz1/2 at 1kHz. The SQUID was mounted on a special chip carrier and was sealed with epoxy resin for protection from humidity. We have developed a 32-channel high Tc SQUID system. We used it to measure magnetic signals of the human heart in a magnetically shielded box. We obtained clear multi-channel magnetocardiac signals, which showed clear so called Q, R, S and T wave peaks. Its clear isofield contour map was also obtained. We could observe activities of a stomach using a tiny steel ball as a tracer. These data indicated that the high Tc SQUID is feasible for these biomagnetic applications.

For real applications of SQUIDs in biomagnetism, geomagnetism and NDE, SQUID devices are required which are stable in a magnetically unshielded environment. We have developed dc and rf SQUID devices with different layouts and widths of Josephson junctions, and have studied their operation in static magnetic fields and unshielded space. Additionally, the noise performance of these SQUID devices has been studied to determine whether there is an influence of the layout or the junction width on noise. Using a wide step-edge junction the transfer function of a washer-type SQUID was not depressed by external magnetic fields up to 3 G. The same stability was obtained using a direct-coupled layout for rf and dc SQUIDs with junctions of width. The best field sensitivity we obtained using a pick-up loop of 8 mm in diameter which was coupled directly to a dc SQUID having an inductance of 150 pH. In magnetic shielding, the field resolution of a SQUID with a single junction resistance of was at 77 K and 1 kHz.

Noninvasive manipulation of biological cells inside a microfluidic channel was demonstrated using a microelectromagnet matrix. The matrix consists of two layers of straight Au wires, aligned perpendicular to each other, that are covered by insulating layers. By adjusting the current in each independent wire, the microelectromagnet matrix can create versatile magnetic field patterns to control the motion of individual cells in fluid. Single or multiple yeast cells attached to magnetic beads were trapped, continuously moved and rotated, and a viable cell was separated from nonviable cells for cell sorting.

We have demonstrated an on-chip magnetic bead transport device based on a set of two tapered current conductors. We have fabricated and tested two types of devices. Both devices are capable of trapping single magnetic microbeads and guiding them along a defined magnetic track. We examined scaling of the basic repetitive element and found good agreement among experiment, theory, and simulations. This novel magnetic transport mechanism opens possibilities for controlled manipulation of magnetically labeled biomolecules.

Alteration of membrane surface charges and membrane Channel activity represents one of the most interesting effects of the electromagnetic exposure on biological structures. Here channel protein activity was recorded in real time by the voltage clamp method. The effect of non-ionizing electromagnetic fields in ultra high frequency (UHF) on the physical behavior of protein, OmpF, was investigated and by our preliminary analysis, we saw these effects in the feature of increasing in voltage sensitivity of this nano pore forming channel. Also increasing the fast flickering of the channel and tendency of the protein to go to the closure state can be considered as the effects of the inserted electromagnetic field.

Atomic magnetometers (AM) are finding many applications in biomagnetism, national security, industry, and science. Fiber-coupled (FC) designs promise to make them compact and flexible for operation. Most FC designs are based on a single-beam configuration or electrical heating. Here, we demonstrate a two-beam FC AM with laser heating that has 5 fT/Hz1/2 sensitivity at low frequency (50 Hz), which is higher than that of other fiber-coupled magnetometers and can be improved to the sub-femtotesla level. This magnetometer is widely tunable from DC to very high frequencies (as high as 100 MHz; the only issue might be the application of a suitable uniform and stable bias field) with a sensitivity under 10 fT/Hz1/2 and can be used for magneto-encephalography (MEG), magneto-cardiography (MCG), underground communication, ultra-low MRI/NMR, NQR detection, and other applications.

We have fabricated a series of highly sensitive spin valve sensors on a micron scale that successfully detected the presence of a single superparamagnetic bead (Dynabeads M-280, 2.8 μm in diameter), and thus showed suitability for identifying biomolecules labeled by such magnetic beads. By polarizing the magnetic microbead on a spin valve sensor with a dc magnetic field and modulating its magnetization with an orthogonal ac magnetic field, we observed a magnetoresistance (MR) signal reduction caused by the magnetic dipole field from the bead that partially cancelled the applied fields to the spin valve. A lock-in technique was used to measure a voltage signal due to the MR reduction. A signal of 1.2 mV rms or 5.2 mΩ of resistance reduction was obtained from a 3 μm wide sensor and a signal of 3.8 mV rms or 11.9 mΩ from a 2.5 μm wide sensor. Micromagnetic simulations were also performed for the spin valve sensors with a single bead and gave results consistent with experiments. Further experiments and simula...