15. Nanomechanical Cantilever Array Sensors

In recent years, mechanics has experienced a revival, as microfabrication technologies and nanotechnology are applied to produce tiny structures. The development of ultraprecise position sensing started three decades ago with a novel imaging technique called atomic force microscopy, which provides ultrahigh topography resolution on the atomic scale by raster-scanning the surface with a microfabricated cantilever beam that has a tiny tip at its free end. The high force sensitivity can not only be used for imaging, but also allows the measurement of surface forces during molecule adsorption processes on the cantilever surface, thus enabling cantilevers to act as chemical sensors. Because of their small size, cantilevers allow fast and reliable detection of small concentrations of molecules in air and solution. In addition to artificial nose and label-free biosensing applications, they have also been employed to measure physical properties of tiny amounts of materials in miniaturized versions of conventional standard techniques such as calorimetry, thermogravimetry, weighing, photothermal spectroscopy and monitoring of chemical reactions. In the past few years, the cantilever-sensor concept has been extended to medical applications and has entered clinics for pilot studies on patients. The small size and scalability of cantilever array sensors might turn out to be advantageous for diagnostic screening applications and disease monitoring, as well as for genomics or proteomics. Using microcantilever arrays allows simultaneous detection of several analytes and solves the inherent problem of thermal drifts often present when using single microcantilever sensors, as some of the cantilevers can be used as sensor cantilevers for detection, and others as passivated reference cantilevers that do not show affinity to the molecules to be detected.