Zhongyang Cheng

Magnetostrictive Microcantilever as an Advanced Transducer for Biosensors

The magnetostrictive microcantilever (MSMC) as a high-performance transducer was introduced for the development of biosensors. The principle and characterization of MSMC are presented. The MSMC is wireless and can be easily actuated and sensed using magnetic field/signal. More importantly, the MSMC exhibits a high Q value and works well in liquid. The resonance behavior of MSMC is characterized in air at different pressures and in different liquids, respectively. It is found that the Q value of the MSMC in water reaches about 40. Although the density and viscosity of the surrounding media affect the resonance frequency and the Q value of MSMC, the density has a stronger influence on the resonance frequency and the viscosity has a stronger influence on the Q value, which result in that, for MSMC in air at pressure of less than 100 Pa, the resonance frequency of MSMC is almost independent of the pressure, while the Q value increases with decreasing pressure. MSMC array was developed and characterized. It is experimentally demonstrated that the characterization of an MSMC array is as simple as the characterization of a single MSMC. A filamentous phage against Salmonella typhimurium was utilized as bio-recognition unit to develop an MSMC based biosensor. The detection of S. typhimurium in water demonstrated that the MSMC works well in liquid.

Design of a surface-scanning coil detector for direct bacteria detection on food surfaces using a magnetoelastic biosensor

The real-time, in-situ bacteria detection on food surfaces was achieved by using a magnetoelastic biosensor combined with a surface-scanning coil detector. This paper focuses on the coil design for signal optimization. The coil was used to excite the sensors vibration and detect its resonant frequency signal. The vibrating sensor creates a magnetic flux change around the coil, which then produces a mutual inductance. In order to enhance the signal amplitude, a theory of the sensors mutual inductance with the measurement coil is proposed. Both theoretical calculations and experimental data showed that the working length of the coil has a significant effect on the signal amplitude. For a 1u2009mm-long sensor, a coil with a working length of 1.3u2009mm showed the best signal amplitude. The real-time detection of Salmonella bacteria on a fresh food surface was demonstrated using this new technology.

Detection of Bacillus anthracis Spores Using Phage-Immobilized Magnetostrictive Milli/Micro Cantilevers

A type of biosensor based on filamentous phage as bioprobe and magnetostricitve milli/micro-cantilever (MSMC) as a sensor platform is developed for in situ detection of Bacillus anthracis spores in water. The phages are immobilized onto the MSMCs surface through physical absorption. It is found that the immobilized phages are attached onto the MSMCs surface through their ends and have a highly packed 2-D configuration. The real-time detection of B. anthracis spores in water with different concentrations was conducted. The experimental results indicate that the smaller the MSMC, the better the detection limit. For example, the detection limit is 104 spores/ml and 105 spores/ml for the MSMCs in size of 1.4 mm × 0.8 mm × 35 μm and 2.8 mm × 1.0 mm × 35 μm, respectively. The SEM observations confirm that the shift in the characteristic frequency of the biosensor is due to the binding of spores on the sensor surface. It is also found that the density of the spores binding at the tip of the cantilever is higher than that in the middle. The specificity of the sensor was studied. It is found that the sensor can detect B. anthracis spores with a much higher binding affinity than the spores of B. cereus and B. megaterium.