研究生科技论文写作,生物医学方向

The Development of Amorphous magnetoelastic sensors Abstract: Freestanding amorphous magnetoelastic (ME) biosensors were fabricated by two ways. One type with larger size, 2000×400×15 mm, 1000×200×15 mm and 500×100×15 mm, was made from an ME Fe40Ni38Mo4B18 ribbon, the other with smaller size 200×40×4 mm was manufactured by dual beam sputtering and non-traditional microelectronic fabrication techniques. Both platforms were immobilized with JRB7 phage and were developed for the real-time in vitro detection of Bacillus anthracis spores. The experimental results show that the measured sensitivity of the ME sensors agrees with theoretical predictions and the specificity of ME sensors coated with JRB7 phage for B. anthracis spore species is excellent. The 200×40×4 mm biosensor was found to have a detection limit of 102 cfu/ml and sensitivity of 13.1 kHz/decade. Keywords: Glasses,metallic; Magnetic properties; Vapour deposition; Biomedical applications;  Environmental applications 1. Introduction A biosensor is an analytical device incorporating a biorecognition element (probe/receptor) with a transducer (platform) system. The specific biological reaction between the bio-recognition element and the target pathogen causes a physical/chemical change at the bio-interface. The transducer/platform converts the observed change (physical or chemical) into a measurable signal that is sent to an output system to be amplified, processed, and displayed [1]. Biosensors offer many advantages in detecting chemicals and foodborne pathogens. They are extremely target specific and sensitive but respond rapidly, making them ideal for real-time detection. Some are even reusable and portable for on-the-spot analysis. Biosensors are now being applied in many fields such as medical care, environmental monitoring, food safety, and the military. Due to the demands from these diverse areas and the development of novel biosensor techniques, the biosensor market is growing and expected to exhibit continuous strong growth. In the next six years,the compound annual growth rate of the biosensor market is estimated to be 11.5% [2]. By 2016, the global revenue for the biosensor market is projected to reach $14 billion [2]. 2. Theory of operation Metallic glasses are non-crystalline alloys with a disordered atomic-scale structure. Their unique microstructure provides excellent mechanical and magnetic properties. The remarkable magnetic softness of metallic glasses originates from the structural magnetic isotropy on a macroscopic scale. Amorphous alloys exhibit high atomic mobility in metastable structures. Therefore, these alloys can be annealed at relatively low temperatures, achieving internal stress relaxation and a dramatic increase in the magnetic softness [2]. Biosensor platforms based on metallic glass materials work on the principle of magnetostriction.Under an applied magnetic field, elastic strains are produced in magnetoelastic (ME) materials resulting in dimensional changes. This property can be used to construct a resonating platform that can be used as the basis for a mass sensor. When an alternating magnetic field is applied to an amorphous magnetoelastic (ME) material, it undergoes a corresponding oscillating shape change that gives rise to a mechanical vibration with a characteristic resonance frequency. This frequency is a function of the shape, physical dimensions, and mass of the sensor platform. If B. anthracis spores bind to the surface of a platform made of ME material (attachment of mass), a drop in the platform resonance frequency will be induced. Changes in the frequency can be measured wirelessly and remotely both in air and in liquid. Based upon this, freestanding ME sensors for the detection of B. Anthracis spores can be developed. Binding of the target analyte can be achieved by immobilizing a selective and specific functional layer on the outer surface of the platform for sensor. The principle for this type of sensor is shown in Fig. 1. Fig. 1. Diagram of the operating principle 3. Structure and main technical A ME biosensor is comprised of a free-standing sensor platform made of a strip-shaped ME resonator and a bio-recognition element (antibody, phage, enzymes, etc.) immobilized on the sensor platform surface. Fig. 2. The principle of operation of ME biosensors The operation principle of the ME biosensor is shown in Fig. 2. A change in the dimensions of the ME material occurs as a result of the alignment of the magnetic domains in the material. The ME materials can efficiently convert the applied magnetic energy into mechanical oscillations with a characteristic resonant frequency by applying a time-varying magnetic field. This mechanical vibration consequently causes an emission of magnetic flux from the resonator. Therefore, the resonator’s resonant frequency, at which the oscillation of the resonator reaches maximum, can be measured remotely and wirelessly by a pick up coil. In the pathogen detection, the biological recognition element immobilized on the ME biosensor surface would capture the interested agents when the biosensor contacts the target species. This results in an increase in mass of the biosensor and a sequential decrease in its resonant frequency. Therefore, the presence of a target pathogen can be detected by monitoring the shift in the resonant frequency of ME biosensors.