Applications of Smart Materials in the Development of High Performance Biosensors
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Applications of Smart Materials in the Development of High Performance Biosensors Z.-Y. Cheng Materials Research and Education Center, Auburn University, Auburn, AL 36849-5341, USA ABSTRACT High performance biosensors are urgently needed from medical diagnosis, to food safety/security, to the war on bio-terrorist. The smart materials play an important role in the development of high performance sensor platform. Biosensors based on microcantilevers have very high sensitivity. The microcantilevers made of different materials, such silicon, piezoelectric and magnetostrictive materials, are discussed and compared in this paper. The magnetostrictive-based microcantilevers exhibit the best performance among all microcantilevers. A new sensor platform – magnetostrictive particles (MSPs) – is reported. The advantages of MSPs over microcantilevers are experimentally demonstrated. The MSPs are wireless/remote sensors, which makes it is possible to employ the MSP-based biosensors in different environments/media. The fabrication of MSPs in micro to nano-scale is reported. Compared with the microcantilevers, MSPs exhibit a better mass sensitivity and a higher Q value, which make the MSPs a much higher overall sensitivity. INTRODUCTION The ability to identify the presence of a very small number of target proteins, bacteria, or spores in a small volume of liquid would greatly advance scientific research into the human genome, provide a more sensitive tool for medical diagnostics and protection against bioterrorism. Immunosensors (or biosensors) are considered as having great potential for future pathogen detection due to their extreme sensitivity and near real-time detection capability. Much research is currently being conducted on biosensors that utilize microcantilevers (MCs) and other acoustic wave (AW) devices as sensor platforms due to the fact that the AW device as a sensor platform offers the capability for real-time detection and many other advantages, such as simplicity and low cost [1-3]. For biodetection, the AW device as sensor platform is usually immobilized with a bio-molecular recognition layer, such as antibody, as probe on its surface to react with the target species [3,4]. The reaction of probe with the target species results in a change in the recognition layer, such as the mass. The principle of these AW-based biosensors is based on a fundamental feature of the AW device as a resonator – the resonance frequency of the device changes with the mechanical load, such as mass. Therefore, the performance of these AW devices is characterized using two parameters: 1) the mass sensitivity (Sm), which describes the shift in resonance frequency due to the attachment of a unit mass onto the surface of the device; 2) the mechanical merit factor (Q value), which defines the sharpness of the resonance peak. A higher Q value means a sharper resonance peak, which would result in a higher precision in determining resonance frequency and a smaller minimum detectable frequency change. Therefore, for developing high
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