Electrical conductivity measurements chemical sensors

Capacitance-based chemical sensors are in the class of devices that transduce analytes into electrical currents. Such sensors are typically comprised of a dielectric, chemically-sensitive film coated onto a substrate electrode these films pass low conduction current, making amperometric or conductimetric measurements less sensitive or attractive for signal transduction. To detect an analyte, changes in the chemically-sensitive film s capacitive properties (associated with its dielectric constant, charge uptake, or formation of interface dipole layers) are measured when an active species is present or generated. 

Conductivity. Electrical conductivity measurements are appealingly simple and sensitive, and reflect the charge carrying ability (carrier population and mobility) of a test medium Interposed between two electrodes biased by DC or AC potentials. The key for chemical sensoring is to design some element of chemical selectivity Into the values of carrier population or mobility. Measurements in liquid ionic solutions (the classical method of conductimetry) have little intrinsic... 

Sensors are used to record the sensitivity with a change in parameters and then measured based on electrical resistivity, chemical activity, magnetic permeability, thermal conductivity, and capacitance. Sensors based on nanoparticles are capable of detecting very small amounts of chemical vapors with the help of detecting elements based on their microstmcture electrical characteristics, such as resistance or capacitances when they absorb a gas at low concentration. 

Although we believe that the importance of IS is demonstrated throughout this monograph by its usefulness in the various applications discussed, it is of some value to summarize the matter briefly here. IS is becoming a popular analytical tool in materials research and development because it involves a relatively simple electrical measurement that can readily be automated and whose results may often be correlated with many complex materials variables from mass transport, rates of chemical reactions, corrosion, and dielectric properties, to defects, microstructure, and compositional influences on the conductance of solids. IS can predict aspects of the performance of chemical sensors and fuel cells, and it has been used extensively to investigate membrane behavior in living cells. It is useful as an empirical quality control procedure, yet it can contribule to the interpretation of fundamental electrochemical and electronic processes. 

Conductometric sensors, measuring the variatimi of the solution conductance due to electrical charge concentrations changes. The method is simple but not selective, since the conductance depends on the ionic concentration of all of the present species. In view of the fact that no electrochemical processes take place, conductometric sensors are not strictly electrochemical ones. They are considered, according to lUPAC chemical sensors definitions and classification [1], as a subclass of electrical devices in which the signal results from the change of electrical properties caused by the interaction of the analyte. Nevertheless, electrical devices are frequently put into one category with the electrochemical devices [1]. 

Yet another emerging application for electrically conductive polymer materials is biosensors and chemical sensors, which can convert chemical information into a measurable electrical response. Abtech Scientific Inc. in Yardley, Pa., is making chemical transducers from mostly polyaniline as well as polythiophene and polypropylene for analytical applications in which one measures conductivity and as a result infers what the chemical composition is. In other words, a very small change in the redox composition brought about by small quantities of a range of chemicals can induce a large, rapid change in electrical conductivity. 

This method is primarily based on measurement of the electrical conductance of a solution from which, by previous calibration, the analyte concentration can be derived. The technique can be used if desired to follow a chemical reaction, e.g., for kinetic analysis or a reaction going to completion (e.g., a titration), as in the latter instance, which is a conductometric titration, the stoichiometry of the reaction forms the basis of the analysis and the conductometry, as a mere sensor, does not need calibration but is only required to be sufficiently selective. 

Because of their electrical, optical, and redox properties as well as the thermal and chemical stability, the Pcs also have been tried in the detection of volatile organic compounds and poisonous gases, which is very important for environment and human health. In the past decades, the possible applications of Pc thin film as sensor for atmospheric gaseous pollutants have been extensively studied [73, 74], Langmuir-Blodgett films of some multinuclear and multidouble-decker lutetium Pcs have also been used for those measurements [75,76], More details about conductivity and sensing properties of Pcs can be found elsewhere [77,78]. 

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