Analysis, control and augmentation of microcantilever deflections in bio-sensing systems

The main causes for the deflection of microcantilevers embedded in micromechanical biodetection systems are investigated. The primary deflection due to the chemical reaction between the analyte molecules and the receptor coating, which produces surface stresses on the receptor side is analyzed. Oscillating flow conditions, which are the main source of turbulence, are found to produce substantial deflections at relatively large frequency of turbulence. Bimaterial effects influencing the microcantilever deflections are established analytically, and found to be prominent at a relatively low frequency of turbulence. In the absence of bimaterial effects, turbulence increases the deflection due to chemical reactions at relatively large frequency of turbulence yet it increases the noise due to the increased dynamical effects of the flow on the microcantilever. The mechanical design and optimization of piezoresistive cantilevers for detecting changes in surface stress via finite element analysis is also discussed. The introduction of stress concentration regions (SCR) during cantilever fabrication greatly enhances the detection sensitivity. Biosensing experiments based on resonance frequency shift are presented, which show that the results strongly depend on the interaction of specific analytes with the receptor surface. Finally, novel microcantilever assemblies are presented for the first time that can increase the deflection due to chemical reaction while decreasing those due to flow dynamical effects. (C) 2003 Elsevier Science B.V. All rights reserved.