Silicon microcantilevers as sensors

Babita Dhayal, Purdue University

Abstract

This work focuses on the general use of microcantilever arrays for parallel detection of multiple analytes and understanding the mechanics behind it. The system employs an array of eight silicon micro cantilevers and has the capability of measuring cantilever deflection due to differential surface stress generated as well as frequency change due to added mass in both gaseous and liquid environments. In this work, we move beyond antibody-antigen binding systems and demonstrate that short peptides ligands can be used to efficiently capture Bacillus subtilis and Bacillus anthracis spores in liquids, given that specific peptides corresponding to the particular bacteria are synthesized. These peptide functionalized cantilever array can be stored under ambient conditions for days without loss of functionality, making then suitable for in-field use. A detailed experimental protocol, optimizing every step is presented. Applications of this technology can serve as a platform for the detection of pathogenic organisms including biowarfare agents. The dominant physical phenomena producing surface-stress during molecular binding are difficult to specify a priori. Differential surface stress generated due to adsorption of small molecules on gold coated cantilevers is measured to gain insight into the mechanisms involved in the self-assembly process and into the origin of associated the surface stress. Our experiments indicate that the contribution from inter-molecular Lennard-Jones interactions and binding energy between the end group and the functionalized surface play a minimal role in the development of surface stress. Electrostatic repulsion between adsorbed species stress and Changes in the electronic structure of the underlying gold substrate play an important role in surface stress generation. To achieve higher sensitivity in the performance of cantilever sensors, optimized cantilevers of different dimensions are required. By adjusting cantilever dimensions, it is possible to optimize one important parameter called the quality factor. Such a procedure is both costly and time consuming. We show that by simply adding localized mass along the length of a cantilever, the quality factor of the cantilever can be improved. A theory explaining the data is presented.

Degree

Ph.D.

Advisors

Reifenberger, Purdue University.

Subject Area

Physics|Condensed matter physics

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