Date of Award
Doctor of Philosophy
Michael J. Sepaniak
Kelsey Cook, Robert Hinde, Panos Datskos
Microcantilever (MC) based chemical sensors have become more widely used during the past 10 years due to the advantages they possess over other chemical sensors. One of the most significant characteristics is their extremely high surface to volume ratio. This key facet allows surface forces that can be ignored on a macroscale to become a significant sensing transduction mechanism. MC based sensors also exhibit a higher mass sensitivity to adsorbates than do many other chemical sensor platforms. Under many conditions, MC based sensors directly translate changes in Gibbs free energies due to analyte-surface interactions into mechanical responses. However, the widespread application of MCs in the field of sensors has yet to be fully realized. This is primarily due to the lack of a unifying methodology and instrumentation that would allow various research groups to benefit from a combined wealth of knowledge on the subject. The underlying goal of this research is to broaden the depth and scope of knowledge of MC based chemical sensors. By working on several areas in a coherent order, the limitations of MC based sensors have been determined and largely overcome. The information gathered in all aspects of this project will be useful to present and future researchers in this field. The initial research was focused on the application of various chemical films to MC sensors to be able to measure a wide range of chemical species. In one case, thin films of polymeric gas chromatography (GC) phases were deposited onto V-shaped MCs. A main strength to using GC phases was that the responses of the analytes could be predicted before hand by using the McReynolds constants of the phases used. This allowed for the detection and quantification of various chemical species using these moderately selective phases. vi During this phase of research it was discovered that methods for enhancing MC response were needed to overcome some of the traditional problems facing MC based sensors. By employing a new type of underlying nanostructured metallic film, MC response was greatly enhanced. This resulted in a better limit of detection and wider dynamic range relative to previous results with smooth surface MCs. In addition to advances resulting from nanostructuring, important advances were made in MC coating strategies. The widely used and well-characterized process of physical vapor deposition was used to deposit both organic and polymeric materials onto the MC surface. This process allowed for uniform films to be deposited with tailored thicknesses and for individual MCs on a single chip to be coated selectively. Another approach involving the immersion of MCs into fused silica capillaries containing solutions of thiolated materials was also developed. This method also allowed for individual MCs in an array to be selectively coated. Finally, out of these results and a developing trend of using sensor arrays came the need to increase the robustness and selectivity of MC based systems. Two different systems for achieving these goals were developed. First, a simple differential system based upon dual diode lasers was constructed in order to eliminate common sources of noise and non-specific interactions that decrease the dynamic range of these sensors. This system was also applied to the quantification of individual components in a binary mixture. While this system has met only limited success, it has been a beneficial first step towards MC systems of higher order. Towards that goal, a system designed to measure multiple MCs simultaneously using an array of vertical cavity surface emitting lasers was also used. This system measures the responses of multiple MCs exposed to an vii analyte in a single run and provides unique response patterns for that analyte. This allowed for the qualitative analysis of a simple mixture to be performed.
Tipple, Christopher, "Strategies for Enhancing the Performance of Chemical Sensors Based on Microcantilever Sensors. " PhD diss., University of Tennessee, 2003.