Xue-cheng Sun

Meander-shaped magnetoimpedance sensor for measuring inhomogeneous magnetic fringe fields of NiFe films

Magnetic fringe fields of NiFe films were measured by giant magnetoimpedance (GMI) sensor, in this work. We have observed an interesting GMI phenomenon: the impedance enhanced first and then declined due to the presence of NiFe films, it is suggested that magnetic fringe fields have strengthened the longitudinal external magnetic field. Results indicated that the GMI sensor was able to quantify the magnetized NiFe films from 1 × 5 to 5 × 5 mm2. Anyway, this study has extended the application of GMI sensor to film detection, which makes it promising in detecting the defects of soft magnetic devices.

Improved Performance of Integrated Solenoid Fluxgate Sensor Chip Using a Bilayer Co-Based Ribbon Core

In this paper, based on the multiwire core design and microelectromechanical system technology, we report improved performance of a microsolenoid fluxgate sensor by integrating a bilayer core of co-based amorphous ribbon. By means of utilizing integrated multilayer core structure and high permeability amorphous ribbon core material, this paper shows how a high-performance microfluxgate chip with small dimensions can be realized. The fabricated sensors exhibit a best sensitivity of 3165 V/T, a power of 183.2 mW and a linear range of 150 μT at 100 kHz. The noise power density is found to be 0.5 nT/Hz1/2 1 Hz and the noise rms level is 2 nT in the frequency range of 25 mHz-10 Hz.

A GMI biochip platform based on Co-based amorphous ribbon for the detection of magnetic Dynabeads

We describe a giant magnetoimpedance (GMI) biochip platform for the detection of streptavidin-coupled magnetic Dynabeads of different sizes. The GMI sensor based on micro-patterned Co-based amorphous ribbons (Metglas® 2714A) with a meander structure was fabricated by micro-electro-mechanical-systems (MEMS) technology. A gold film was then deposited on the GMI element to act as a support platform for immobilizing various concentrations of magnetic Dynabeads (1 μm and 2.8 μm). The results indicate that Dynabeads of 1 μm in diameter with a concentration as low as 5 μg mL−1 can be detected by using the ribbon-based GMI sensor, and that the detection limit for Dynabeads of 2.8 μm diameter was 1 μg mL−1. Besides, using the same number of magnetic Dynabeads with different sizes, the GMI responses were significantly enhanced after coating the 2.8 μm Dynabeads. The ribbon-based micro-integrated GMI biosensor is easy to fabricate and is expected to be used for the detection of very low concentrations of Dynabead-labeled biomarkers.

A Dynabeads-labeled immunoassay based on a fluxgate biosensor for the detection of biomarkers

Magnetic bead-based biosensors are becoming a hot spot in biomedical fields. A Dynabeads-labeled immunoassay has been developed using a micro fluxgate biosensor for the detection of alpha fetoprotein (AFP) and carcinoembryonic antigen (CEA). The micro fluxgate sensors with a rectangular permalloy core with sides of equal width and three-dimensional solenoid coils are fabricated by micro-electro-mechanical-system (MEMS) technology, including thick photoresist lithography and electroplating. The immune reaction of biomarkers is accomplished on a separated Au film substrate surface with a self-assembled layer. Sandwich immunoassay is used to specifically capture and label the biomarker. Dynabeads are conjugated into the biomarker by a streptavidin–biotin system. The micro fluxgate-based sensing system was characterized firstly in different concentrations of Dynabeads. It is found that a concentration as low as 0.1 μg ml−1 (90 Dynabeads) can be detected by this sensing system with an external magnetic field in the range of 643 μT to 1180 μT. The AFP and CEA with different concentrations were detected by the sensing system. The results reveal that a minimum detectable concentration of 1 pg ml−1 was achieved in the measuring ranges of 724 μT to 1150 μT for AFP, and 670 μT to 1110 μT for CEA. Compared with a micro fluxgate sensor with a ribbon core for the detection of biomarkers, the micro fluxgate sensor with an electroplated permalloy core possesses a wider linear measuring range, and could make it possible to integrate a micro fluxgate-based biosensing system produced on a large scale, with an expanded application field and reduced costs.

Detection of Dynabeads in small bias magnetic field by a micro fluxgate-based sensing system

The micro fluxgate sensors have shown high sensitivity for the magnetic beads detection. For portable magnetic biological detection, Co-based amorphous ribbons with high permeability and low saturation magnetic induction are chosen as core materials to lower the operation requirements of the fluxgate-based magnetic beads detection. The micro fluxgate sensors with single-layer core and bi-layer core are fabricated by Micro-Electro-Mechanical System technologies, which exhibit a power consumption of 10.88 mW and 24.48 mW, a sensitivity of 1644 V/T and 1456 V/T, and a noise of 1.66 nT/Hz1/2@1 Hz and 2.32 nT/Hz1/2@1 Hz, respectively. The Dynabeads with concentrations of 300 μg/ml in 10 μl are detected by the micro fluxgate-based sensing system based on static response, and the results show signal change ratio of 12.2% and 9.2% under the max signal difference at 215 μT and 480 μT of the bias magnetic field for two kinds of the sensors, respectively, which is near the saturation point of the sensors. The fluxga...

An integrated microfluidic system using a micro-fluxgate and micro spiral coil for magnetic microbeads trapping and detecting

We report an innovative integrated microfluidic platform based on micro-fluxgate and micro-coils for trapping and detecting magnetic beads. A micro-spiral coil fabricated by microfabrication technology is used to trap the magnetic beads, and the micro-fluxgate is employed to detect the weak magnetic field induced by the trapped magnetic beads. The fabrication process of the magnetic bead trapping system using a micro-coil is highly compatible with that of the micro-fluxgate sensor, making fabrication of this integrated microfluidic system convenient and efficient. It is observed that the magnetic bead trapping ratio increases as the number of magnetic beads is increased with a flow rate of 5 to 16.5 μL·min−1. Samples spiked with different concentrations of magnetic beads can be distinguished clearly using the micro-fluxgate sensor in this microfluidic system. In this study, the results demonstrate that the microfluidic system traps and detects magnetic beads efficiently and is a promising candidate for biomarker capture and detection.

Detection of alpha-fetoprotein via a magnetic-beads-based sandwich immunoassay combined with giant magnetoimpedance biochip

This article deals with the design of an integrated giant magnetoimpedance biochip combined with a sandwich immunoassay for the detection of alpha-fetoprotein, and we have offered the possible physical origins of the enhanced giant magnetoimpedance responses caused by Dynabeads. The giant-magnetoimpedance-based magnetic immunoassay showed a good sensitivity and specificity for the detection of 3 ng/mL alpha-fetoprotein. We also observed that there was significant difference in detection sensitivity between two giant magnetoimpedance biochips, which is probably related to the electroplating instability. Such an integrated giant magnetoimpedance biochip could be extended for the detection toward a wide spectrum of target biomolecules and shows promising potential for clinical applications.

Effect of annealing orientation on the giant magnetoimpedance in micro-patterned Co-based ribbon

Cobalt-based amorphous ribbons (Metglas® 2714A) were annealed treatment with an applied magnetic field. During annealing, the angle between the magnetic field axis and ribbon axis was designed for 0°, 30°, 60° and 90° respectively. MEMS technology was used to fabricate micro-patterned Co-based amorphous ribbons with a meander structure. The giant magnetoimpedance (GMI) effects were observed. The results showed magnetic field annealing treatment can improve the GMI ratio of the ribbon. With the increasing of the angle, the maximum GMI effect of the sample increased. When the angle was 90°, the maximum increment of GMI effect with 46.9 % was got.