Manipulation and controlled amplification of Brownian motion of microcantilever sensors

Microcantilevers, such as those used in atomic force microscopy, undergo Br ownian motion due to mechanical thermal noise. The root mean square amplitu de of the Brownian motion of a cantilever typically ranges from 0.01-0.1 nm , which limits its use in practical applications. Here we describe a techni que by which the Brownian amplitude and the Q factor in air and water can b e amplified by three and two orders of magnitude, respectively. This techni que is similar to a positive feedback oscillator, wherein the Brownian moti on of the vibrating cantilever controls the frequency output of the oscilla tor. This technique can be exploited to improve sensitivity of microcantile ver-based chemical and biological sensors, especially for sensors in liquid environments. (C) 2001 American Institute of Physics.