Date of Award

8-2007

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Mechanical Engineering

Advisor

Jalili, Nader

Abstract

Microcantilever-based biosensors are rapidly becoming an enabling sensing technology for a variety of label-free biological applications due to their extreme applicability, versatility and low cost. These sensors operate through the adsorption of species on the functionalized surface of microcantilevers. The adsorption of biological species induces surface stress which originates from the molecular interactions such as adhesion forces of attraction/repulsion, electrostatic forces or the surface charge redistribution of the underlying substrate. This surface stress, consequently, alters the resonance frequency of the microcantilever beam.
This study presents a general framework towards modeling resonance frequency changes induced due to the surface stress arising from the adsorption of biological species on the surface of the microcantilever. Very few works have dealt with the effect of surface stress on the resonance frequency shifts of microcantilevers and mainly assume a simple model for the vibrating microcantilever beam. In the proposed modeling framework, the nonlinear terms due to beam's flexural rigidity from macro- to micro-scale as well as varying nature of the adsorption induced surface stress are considered.
It is first shown that the nonlinearity of the system originates from two different sources; namely, microcantilever flexural rigidity and adsorption induced surface stress. All these nonlinearities are formulated into the general equation of motion of the vibrating microcantilever. It is then shown that the dynamic mode of biosensing formulated in the paper is much more sensitive than the static mode to the change in the properties of the adsorbed biological species.

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