Architectural considerations of micro- and nanoresonators for mass detection in the presence of a fluid

The sensitivity of various microscale and nanoscale resonator platforms, for use as mass sensors for detection of chemical or biological agents in air or water, is examined in terms of architectural considerations, including shape, scale, vibration mode, and fluid environment. Simple models for estimating damping due to various sources are used to calculate Q for several resonator designs: cantilevers and doubly fixed beams in flexure and extensional bar and disk resonators. The scaling of various contributions to Q is discussed, and the effects of support loss and fluid loss are compared as a function of aspect ratio for beam resonators. The minimum detectable mass is estimated for each of the four resonator designs, both for the case in which additional mass adsorbs uniformly over the resonator surface and the case in which functionalization of the surface is limited in order to maximize sensitivity and minimize added dissipation. The mass sensitivity is best for resonators undergoing extensional motion and worst for flexural devices with high length-to-thickness ratio. The minimum detectable mass is shown to be proportional to scale to the power of 1.75 for microresonator scenarios in which resonator quality factor is limited by viscous damping and proportional to scale squared when the resonator is sufficiently small that continuum fluid models are inappropriate and quality factor is limited by dissipation via momentum transfer to individual fluid molecules. (c) 2008 American Institute of Physics. [DOI: 10.1063/1.3043645]