IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Wednesday Sessions
       Session SS+SC-WeM

Paper SS+SC-WeM6
Adsorption Induced Deflection and Frequency Changes in a Silicon Nitride Cantilever due to Ca@super 2+@ Ions

Wednesday, October 31, 2001, 10:00 am, Room 122

Session: Adsorption on Semiconductor and Metal Oxide Surfaces
Presenter: S. Cherian, Oak Ridge National Laboratory
Authors: S. Cherian, Oak Ridge National Laboratory
A. Mehta, Oak Ridge National Laboratory
T.G. Thundat, Oak Ridge National Laboratory
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Cantilever based micromechanical sensors exploit changes in surface stress due to interactions between the analyte species and cantilever surface. Charged groups on the cantilever surface play a significant role in binding induced deflection of the micro-cantilever. The deflection and frequency response of triangular silicon nitride cantilevers when exposed to calcium chloride solution was investigated in a flow system. The silicon nitride cantilever used was 200µm long and 20µm wide. Calcium chloride solutions of increasing concentrations were injected sequentially into the flow cell and the cantilever response measured. The fundamental resonance frequency of the cantilever shifted to lower values with increasing solution concentrations. The deflections due to interaction with the CaCl@sub 2@ were towards the gold side. The concentration versus deflection curve followed a Langmuir adsorption isotherm. The cantilever response is attributed to chemisorption of calcium ions onto the silicon nitride side. To verify this a calcium binding protein, calmodulin, was used. A cantilever that was exposed to CaCl@sub 2@ solution was subsequently exposed to calmodulin. Calmodulin binding to Ca @super 2+@ ions on the cantilever surface resulted in a deflection. This deflection was significantly different from that observed when calmodulin was exposed onto a fresh cantilever. These observations were further confirmed by fluorescent measurements using a fluorescently tagged calmodulin. These results demonstrate that consideration of ionic interactions of charged species in the medium with cantilever surfaces is critical in interpreting deflection data of cantilever based sensors. This also suggests the importance of passivating one of the surfaces in order to make the deflection of the functionalized cantilever specific to the species of interest.