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David Paul CHEM 248 |
Degrees:
Ph.D., University of Cincinnati, 1981
IR-100 Award, 1985
Research Interests:
chemical sensors
Research:
The development of chemical sensors is our area of general interests. This research usually involves the application of new developments in electronics and transducer design to particular problems in analytical chemistry. Current examples are the development of enzyme electrodes, the application of acoustic wave devices to bioanaytical analysis.
In conjunction with CSTAR, we have been working with the interdisciplinary team of Prof. Yanbin Li, an engineer, and Prof. Michael Slavik, a bacteriologist, to develop biosensors for pathogenic bacteria in food. Faster analysis and lower detection limits for bacteria such as Salmonella are required to meet food safety standards. Current methods of analysis are slow as bacteria need several days to multiply before identification and counting can proceed. We have developed a rapid method of detection for Salmonella by tagging the bacteria with alkaline phosphatase anti-bodies, which when incubated with a phenol phosphate substrate, produce the phenol product at a much faster rate than the native bacteria can reproduce on their own. (see "Rapid Detection of Salmonella Typhimurium Using Immunoelectrochemical Biosensor Coupled with Immunomagnetic Separation", Y-H. Che, Z.,Yang, Y. Li, D.W. Paul, M. Salvik, Journal of Rapid Microbial Methods, 7, 47-59 (1999). The phenol is sensed electrochemically using an enzyme electrode. Research into improving enzyme electrodes for phenol continues at present. Specifically we are developing ways to immobilize the tyrosinase onto the surface of the electrode. The ultimate goal is to develop electrodes which are easy to mass-produce and give similar, and stable responses to phenol.
The thickness shear mode (TSM) acoustic wave sensor experiences an off-resonance frequency shift when mass is applied to its surface. In air or vacuum, the frequency shift is directly proportional to the surface density of the material added to the surface. When used in a liquid, frequency shifts can also result from changes in elasticity experienced by a film. The main limitation of the TSM is that it is blind, responding to mass, viscous and conductivity changes that are within the layer of material probed by the sensor. We over came some of these limitations by developing an electronic oscillator that could not only drive the sensor in a liquid, but also provide in addition to the resonance frequency an automatic gain control (AGC) voltage output which is directly proportional to the energy dissipated by the sensor. (see"An Electronic Oscillator with Automatic Gain Control: EQCM Applications", C.Chagnard, A.N. Watkins, T. Beeler, D.W. Paul, Sensors and Actuators B, 32, 129-136 (1996). The AGC signal provides an additional measurement to probe thin films and the selective coatings placed over the sensor by measuring changes in the elasticity and the dielectric properties experienced during analyte up-take. Applications include a direct sensor for cholesterol. ("Response of a Thickness-Shear-Mode Acoustic Wave Sensor to the Adsorption of Lipoprotein Particles", S. Snellings, J. Fuller, D.W. Paul, Langmiur, in Press)