Stability, chemical sensors

His research interests are generally in high-temperature and solid-state chemistry of materials, including electrochemical devices (e.g., chemical sensors and fuel cells) and the chemical stability of materials (e.g., high-temperature oxidation). Dr. Fergus is an active member of the Electrochemical Society, the Metals, Minerals and Materials Society, the American Ceramics Society, the Materials Research Society, and the American Society for Engineering Education. 

This atmospheric stability versus friction velocity plot is capable of representing any atmospheric condition except that when the stability is neutral. The information contained in Figure 1 and equation 2 allows the relationship between the value of the surface flux and the required chemical sensor resolution to be estimated for a full range of atmospheric conditions. 

There are, however, several fields of current research in which a corresponding level of understanding would be of interest also for large molecular adsorbates. For example, adsorbate-substrate interactions are relevant in the general areas of biocompatibility [51] and chemical sensors [52]. The requirement of dye-sensitization of metal oxide semiconductors also makes this an important aspect of many molecular photovoltaic devices. In fact, a good interfacial contact between dye and substrate, characterized by long-term stability and intimate electric contact, is vital for the efficiency of e.g. the dye-sensitized solar cells which have been at the center of our attention for the last five years. 

In general, traditional electrode materials are substituted by electrode superstructures designed to facilitate a specific task. Thus, various modifiers have been attached to the electrode that lower the overall activation energy of the electron transfer for specific species, increase or decrease the mass transport, or selectively accumulate the analyte. These approaches are the key issues in the design of chemical selectivity of amperometric sensors. The long-term chemical and functional stability of the electrode, although important for chemical sensors as well, is typically focused on the use of modified electrodes in energy conversion devices. Examples of electroactive modifiers are shown in Table 7.2. 

Sensing chemical species is a much more difficult task than the measurement of mechanical variables such as pressure, temperature, and flow, because in addition to requirements of accuracy, stability, and sensitivity, there is the requirement of specificity. In the search for chemically-specific interactions that an serve as the basis for a chemical sensor, investigators should be aware of a variety of possible sensor structures and transduction principles. This paper adresses one such structure, the charge-flow transistor, and its associated transductive principle, measurement of electrical surface impedance. The basic device and measurement are explained, and are then illustrated with data from moisture sensors based on thin films of hydrated aluminum oxide. Application of the technique to other sensing problems is discussed. 

Both organic and inorganic polymer materials have been used as solid supports of indicator dyes in the development of optical sensors for (bio)chemical species. It is known that the choice of solid support and immobilization procedure have significant effects on the performance of the optical sensors (optodes) in terms of selectivity, sensitivity, dynamic range, calibration, response time and (photo)stability. Immobilization of dyes is, therefore, an essential step in the fabrication of many optical chemical sensors and biosensors. Typically, the indicator molecules have been immobilized in polymer matrices (films or beads) via adsorption, entrapment, ion exchange or covalent binding procedures. 

The stoichiometry is therefore controlled by the composition of the guest mixture. The compounds are isostructural with respect to the location of the host molecules, and the guests lie in essentially the same sites and are partially disordered. This is an important result, in that the ratio of the guests can be controlled, and this phenomenon has implications for crystal engineering. Thus, the physical and chemical properties of such compounds can be governed, and this has significance in such fields as chemical sensors, optical and electronic properties of organic crystals, as well as their thermal stabilities and kinetics of desolvation. 

In conclusion, we believe molecular imprinting can be usefully combined with electrochemical transducers to produce new chemical sensors that exhibit selectivity, sensitivity and great stability and tolerance of harsh environments when compared with biosensors. 

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