Application to chemical sensors

The interaction of carbon nanotnbes with their environment, and in particular with gases or liquids adsorbed either on their internal or external surfaces, is attracting increasing attention dne to the possible infinence of such adsorption on the CNT electronic properties (application to chemical sensors) and to the possibility of nsing these materials for efficient gas storage or for gas separation [11]. 

Rabe J, Buttgenbach S, Schroderr J, Hauptmann P (2003) Monolithic miniaturized quartz microbalance array and its application to chemical sensor systems for liquids. IEEE Sens J 3 361-368... 

Polythiophenes (PTs)/CNTs composites have emerged as an intriguing system for use as photovoltaic devices and field effect transistors [57]. Swager and Bao independently reported methods for the assembling of PTs/CNTs systems and showed their great potential as transparent conductive films [58]. Another interesting application arises from the possibility to functionalize the polythiophene backbone for applications as chemical sensors [134]. 

In the following, the concept of micro modular process engineering is introduced together with the backbone interface developed in order to realize this modular approach. The integration of sensors and an electronic bus system is also described, and the physical characterization of the backbone is discussed within a case study of the enantioselective synthesis of organoboranes. Within the second case study, the sulfonation of toluene with gaseous sulfur tri oxide, the backbone system together with the micro structured devices used is finally assessed based on its application to chemical synthesis. 

Potential applications of chemical sensors are diverse and numerous, and the environment where the sensor is used varies. Therefore, chemical sensor often requires to be tailor-made or semi-tailor-made to meet the needs in the special circumstance. For example, sensing of oxygen in an automobile exhaust or in water or in blood can be accomplished by using an electrochemical-based sensor. However, the selection of electrolyte and a diffusion-limited layer or protective membrane will be different in each case. Therefore, the platform chemical sensor technology is discussed in general. Special applications of a chemical sensor under a particular circumstance need to be addressed separately. 

The application of chemical sensors now and in the future will be oriented around real time monitoring of chemical and environmental processes [3, 4]. These processes are complex systems where a variety of chemicals are present. From a calibration point of view, sensor systems for these applications will either have to be fully selective or be able to handle multicomponent samples. Since the perfectly selective sensor is difficult to almost impossible to develop, sensors in the array or two-dimensional array format have certain advantages. 

The basic characteristics of chemical sensors and biosensors—including high specificity and sensitivity, portability, real time output, cost effectiveness, and user friendliness—make them applicable to virtually every major product market. The immediate market targets for these sensors are in medical diagnostics, detection and alarm systems, environmental monitoring, and food processing. Future markets include application of chemical sensors and... 

There are a myriad of applications for chemical sensors, and one important area is the detection of toxic gases and vapors. Toxic industrial chemicals and materials (referred to as TICs and TIMs) represent one class of materials for which chemical sensors are designed and applied. Chemical warfare agents (CWAs) are another set of materials for which chemical sensors are used, and they represent one of the most challenging groups of analytes due to their extreme toxicity, which translates to a very low required detection limit. Detection of explosives additionally requires high sensitivities due to the low vapor pressures of the explosive materials (order of magnitude 6 x 10-6 Torr for TNT and 5 x 10 9 Torr for RDX). 

In addition to chemical sensors, DNAzymes have found applications in molecular logic gates [68-70] and molecular motors [71, 72],... 

Electrically conductive polymers are perspective materials in modern technologies because of their potential applications as chemical sensors, catalysts, microelectronic devices, etc. [1]. The interest to new hybrid nanostructured materials based on polymer matrix with poly-7t-conjugated bonds and noble metals nanoparticles constantly increases. This is reasoned by a wide spectrum of new optical and electrophysical properties [2]. 

Another most interesting approach proposed to improve chemical interactions and reduce the operating temperature is optical excitation. High temperatures limit the application of chemical sensors to nonexplosive and inflammable environments. As photons above the bandgap are absorbed by metal oxide semiconductors, free carriers are produced in the space charge area. The excess electrons are swept away from the surface, while excess holes are swept towards it due to the electrical field in the space charge... 

Significant efforts have been made to develop and test new metal oxides. However, the application of chemical sensors still faces problems such as selectivity and long-term drift due to stoichiometry changes and coalescence of crystallites. The notion of preparing multipurpose devices has been replaced by the development of sensors tailored for specific and focused applications. 

Another area of intense interest in conducting-polymer nanomaterials for chemical sensing is their combination with carbon nanostructures, most particularly carbon nanotubes, either single-walled (SWNT) or multiwaUed (MWNT). This again reflects the desire to combine the beneficial properties of both types of material to create new combinations with novel properties. CNTs empart high conductivity and high aspect ratios, which yield low percolation thresholds with nanodimensional stmctural order. This has led to their application as chemical sensors. However, CNT-based devices are difficult to fabricate, an issue which may be overcome by their dispersion in a conductive polymeric matrix. 

This discussion is mainly limited to measurements of temperatures and strains, but fibre optic sensors are used in many other applications, as chemical sensors, electrical fields, etc. A global review can be found in Lopez-Higuera (2002). 

Interest in organometallic maaomolecules has grown exponentially ever since Arimoto and Haven first polymerized vinylferrocene in 1955 [1]. Organometallic polymers are known to possess unique optical, magnetic, and thermal properties which allow for potential applications as chemical sensors, electrocatalysts, modified electrodes, and photo-active molecular devices [2-7]. Organoiron polymers are one of the most prevalent classes of organometallic polymers, with many reports on their synthesis and properties published over the past 50 years [8-11]. Of the many varieties of organoiron species, ferrocene and cationic cyclopentadienyliron complexes are most commonly incorporated into polymers. 

Based on conducting polymer nanomaterials, various apphcations are reviewed in the final section. These applications include chemical sensor and biosensor, transistor and switch, data storage, supercapacitor, photovoltaic cell, electro chromic device, field emission display, actuator, optically transparent conducting material, surface protection, and substituent for carbon nanomaterials (Fig. 1). Because large amounts of research have been dedicated to this field, it is very difficult to cover whole apphcation fields of conducting polymers. Some comprehensive review articles related to applications of conducting polymers are available [67-73]. 

Recently, the application of PS to chemical sensors has been considered [254-256]. The main advantages of this material for gas sensor and actuator applications are a unique combination of (i) a crystalline structure, (ii) a huge internal surface (200-500 m cm" ) [218, 257] that enables one to enhance the adsorbate effects, and (iii) a highly reactive surface, allowing efficient modification of the PS surface by various treatments such as contact with organic solvent, thermal annealing, or an illumination. 

Because EPs can be formed and modified electrochemically their application to electrochemical sensors is the natural choice. It is again the remarkable flexibility of their design which makes them universally applicable if necessary they can be prepared with the high conductivity needed for amperometric sensors. They also form well defined ohmic contacts with the metal electrodes required for conductimetric sensors. Their thickness, which is important in potentiometric sensors, can be controlled. We now take a more detail look at the three principal transduction electrochemical modes. A good source of information on electrochemical aspects of EPs is the review chapter on chemically modified electrodes by Murray [3]. 

This work describes recent advances in the preparation of hydrogen bond acidic polycarbosilanes and their application as chemical sensor coatings. We have prepared hydrogen bond acidic polymers based on polycarbosilanes with the goal of improving upon the chemical and thermal properties of this class of functionalized polymer (3-5). Results pertaining to the preparation of selected model compounds are also described. 

As mentioned above, design, microfabrication, testing and application of devices of this kind is undergoing an explosive growth phase (Reyes 2002 Auroux 2002 Vilkner 2004 Dittrich 2006 Whitesides 2006). Some authors prefer to distinguish between jl-TAS and lab-on-a-chip systems. The former correspond to chemical sensors requiring no external ancillary devices other than... 

A sensor is a device that responds to an external stimulus with a measurable response. In this chapter, we restrict our discussion to sensors that respond to chemical species, including oxygen and water vapor (humidity). There are many applications of chemical sensors, including monitoring gas-phase species for air quality and safety applications, and measuring pH or other ion concentrations in water samples. Sensors also find use in healthcare, forensic, security, and consumer product applications. 

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