Pollution chemical sensor development

The current research focus within the sensor development field seems to be concentrated on miniaturization while incorporating multiple quantitative analytical capabilities. Other high-demand characteristics are shorter response time, minimal hardware requirements, multiple analyte and media capabilities, and improved sensitivity, selectivity, and specificity (Zemel 1990). Advancements and improvements for both biological and chemical threat agent sensors will have numerous other benefits to diverse applications, such as quality and process control, biomedical analysis, medical diagnostics, fragrance analysis, environmental pollution monitoring, and control forensics. 

Here, the product species NO2 is produced in an excited electronic state and emits light in the visible-near IR region. It has been found that the intensity of the chemiluminescence is proportional to the concentration of NO in the ppm- ppb range. Thus, the reaction shown in Equation [32] can be used as the basis for the development of a chemical sensor for NO. The detection of NO is important because nitric oxide is a chief environmental pollutant, and also because NO plays an Important role in human biology. 

One of the major breakthroughs in nanotechnology is the use of nanomaterials as catalysts for environmental applications [149]. Nanomaterials have been developed to improve the properties of catalysts, enhance reactivity towards pollutants, and improve their mobility in various environmental media [150]. Nanomaterials offer applications to pollution prevention through improved catalytic processes that reduce the use of toxic chemicals and eliminate wastes. Nanomaterials also offer applications in environmental remediation and, in the near future, opportunities to create better sensors for process controls. 

Application of chemiluminescence to chemical analysis has been developing since the latter half of the 1950s. This method has many advantages, e.g., high sensitivity, good selectivity, linearity in a wide concentration range, and quick response. It has also been used for the measurement of air pollutants. This method, however, requires a supply of reactants to produce luminescent species through chemical reaction. This is a difficult point for the application of this method to gas sensors. 

Several challenges remain for the ultimate practical use of these sensors. The response time of the solid state sensors are short (seconds) for initial sensing, but recovery times range from minutes to hours at room temperature. The stability of the sensor to drift associated with accumulation of fixed charge at interfaces, as well as the high sensitivity to ubiquitous urban pollutants ozone and N02 are problematic. All MPc OTFTs show some response to moisture, and conductivity is also temperature sensitive so that humidity and temperature compensation are essential. On a basic research level, the detailed characterization of charge trapping states, electronic structure, and the interactions with analytes is not yet fully understood on a quantitative theoretical basis. The time response of sensor initiation and recovery is also not understood in a detailed manner. In spite of these limitations, the intrinsic chemical stability of MPc compounds and their compatibility with microsensor array fabrication make these candidate OTFTs for further research and development. 

---