Means of performing determinations by conventional electrochemical methods on solid samples in the absence of a liquid have been described recently. Proposed is the application of this methodology to the design of a new type of sensor for gas-phase species. Electrode arrays on wafers will be coated with ionically-conducting films by sol-gel chemistry. Upon contact with gases that are redox-active electrochemically, an amperometric response related to the concentration of the targeted species is predicted. The inter-relationship among the applied potential, film composition, sample humidity, and the presence of multiple electroactive components in the gas will be investigated. The test species of interest in this study will require catalysts to promote the electrode process and/or to guide the electrode reaction toward products that do not foul the electrode surface. The investigation will consider three types of catalysis, namely modification of the indicator electrode surface by redox mediators, impregnation of the film with complexes that are known from solution chemistry to be active catalysts, and using sol-gel chemistry to incorporate redox mediators in the backbone of the solid films. An important hypothesis is that these solids (called """"""""xerogels"""""""" when prepared by drying under ambient conditions) will support electrocatalysis in a manner comparable to liquid phase experiments. Critical to the successful development of these sensors are finding means of buffering the xerogels and of measuring the pH therein. An ability to control the pH in xerogels is projected to be a major advantage over an alternative design of using organic ionomers as the electrolyte. In addition, on the basis of preliminary work, the xerogel matrix is hypothesized to provide amperometric responses that are independent of humidity over a wide range, which is a second advantage over organic ionomers as solid electrolytes. The test species will include CO, CO2, NH3, ethanol, and selected amines. The proposed sensors will permit their determination in air samples and in vapors above liquids. The latter strategy is projected to be applicable to study of biological fluids and other clinical samples without direct contact of the sensor to the sample. An improved means of monitoring products of enzymatic reactions also is an anticipated outcome.
| Holmstrom, S D; Cox, J A (2000) Electrocatalysis at a conducting composite electrode doped with a ruthenium(II) metallodendrimer. Anal Chem 72:3191-5 |
| Tess, M E; Cox, J A (1998) Humidity-independent solid-state amperometric sensor for carbon monoxide based on an electrolyte prepared by sol-gel chemistry. Anal Chem 70:187-90 |
