Tailoring beam mechanics towards enhancing detection of hazardous biological species

Microcantilever based sensors have been widely employed for measuring or detecting various hazardous chemical agents and biological agents. Although they have been successful in detecting agents of interest, researchers desire to improve their performance by enhancing their mass sensitivity towards developing "detect to warn" detection capabilities. Moreover, there has been little work aimed at tailoring beam mechanics as a means to enhance mass sensitivity. In this paper, a numerical study is performed to assess the influence of microcantilever geometry on mass sensitivity in order to improve these devices for better detection of hazardous biological agents in liquid environments. Modal analysis was performed on microcantilevers of different geometries and shapes using ANSYS software and compared to the basic rectangular shaped microcantilever structures employed by most researchers. These structures all possessed a 50 mu m length, 0.5 mu m thickness and 25 mu m width where the cantilever is clamped to the substrate, and were analyzed for their basic resonance frequency as well as the frequency shift for the attachment of a 0.285 pg of mass attached on their surfaces. These numerical results indicated that two parameters dominate their behavior, (1) the effective mass of the cantilever at the free end and (2) the clamping width at the fixed end. The ideal geometry was a triangular shape, which minimized effective mass and maximized clamping width, resulting in an order of magnitude increase in mass sensitivity (1,775 Hz/pg) over rectangular shaped cantilevers (172 Hz/pg) of identical length and clamping width. The most practical geometry was triangular shaped cantilever with a square pad at the free end for capturing the agent of interest. This geometry resulted in a mass sensitivity of 628 Hz/pg or nearly a 4-fold increase in performance over their rectangular counterparts.