AVS 51st International Symposium
    Surface Science Monday Sessions
       Session SS-MoP

Paper SS-MoP29
Selective Detection of Cr(VI) Using a Microcantilever Electrode Coated with a Self-Assembled Monolayer

Monday, November 15, 2004, 5:00 pm, Room Exhibit Hall B

Session: Poster Session
Presenter: F. Tian, Oak Ridge National Laboratory
Authors: F. Tian, Oak Ridge National Laboratory
V. Boiadjiev, University of Tennessee in Knoxville
L. Pinnaduwage, Oak Ridge National Laboratory
G. Brown, Oak Ridge National Laboratory
T. Thundat, Oak Ridge National Laboratory
Correspondent: Click to Email
We have demonstrated detection of Cr(VI) ions using functionalized cantilevers under electrochemical control. Au-coated microcantilever working electrodes are modified with self-assembled monolayer of 4-mercapto-pyridinium in sulfuric acid solution. Differential surface stress changes at the modified microcantilever have been measured to determine Cr(VI) by monitoring the potential-induced deflection of the microcantilever and simultaneous current-potential response by cyclic voltammetry. In an electrolyte containing sulfuric acid alone, the increase of potential causes a compressive surface stress resulting in the microcantilever bending away from monolayer coated Au side. Stressogram (first derivative of stress with respect to potential vs electrode potential) shows sweep rate independence, which is consistent with voltammetry. In the presence of 10@super -4@ M Cr(VI), a compressive stress peak can be observed during cathodic sweep. Surface stress characteristics continue to change during potential cycling at each fix sweep rate although the measured current-potential responses in the voltamogram are still constant. It suggests that there is a strong adsorption of Cr(VI) on pyridinium monolayer coated microcantilever electrode. Because of the adsorption of Cr(VI), the stressogram behavior is only consistent with voltamogram in the very beginning of sweep cycling and at much higher sweep rates. Our results demonstrate that the observed changes of differential surface stress are due not only to potential change, but also to ion adsorption/desorption and electron exchange at the electrode surface. Such potential controlled microcantilever technique offers new insights into the behavior of the solid-liquid interface during electrochemical reactions at modified electrodes.