Catalytic sensor

The operation of a catalytic sensor depends on the oxidation of the flammable gas on the detector which is an electrically heated catalytic filament. This detector is usually made of fine platinum wire that is coated with one of several alternative substances—palladium/platinum/thoria catalysts. These catalysts help to enhance the catalytic activity and prolong the life of the detector by enabling it to operate at lower temperatures. The detector filament is connected to an identical, but inactive, unit in a Wheatstone bridge, and is located adjacent to the active detector. The identical inactive unit allows for ambient temperature compensation. 

Figure 6.2. Sketch of catalytic sensor. (Courtesy of Sensidyne Inc., Clearwater, FL.)...

Many industrial atmospheres contain contaminants such as silicones, organic lead, sulfur compounds, and halogens which can poison catalytic sensors. Manufacturers go to great lengths in the design of these units to minimize loss of sensor activity from such influences.1 Means taken to keep water, corrosive liquids, and dirt from entering sensors involve the installation of membranes before the flame arrestor in front of the detector filament.2... 

Electrochemical sensors are applicable to many toxic gases and are useful for the detection of hydrogen, which is not responsive to the catalytic sensors described earlier. 

Spataru, T., Roman, E. and Spataru, N. (2004), Electrodeposition of cobalt oxide on conductive diamond electrodes for catalytic sensor applications. Rev. Roum. Chim., 49(6) 525-530. 

In principle, this is the best—or at least the simplest—choice for the design of catalytic sensors. They can be directly designed as reagentless devices and no regeneration steps are needed if continuous monitoring is intended. A priori, the catalytic conversion of the analsffe is inherently more selective than any other approach. Optimally, the sensor response should be limited by mass... 

Thermometric sensors are based on the measurement of the heat effects of a specific chemical reaction or an adsorption process that involves the analyte. In this group of sensors the heat effects may be measured in various ways, for example in catalytic sensors the heat of a combustion reaction or an enzymatic reaction is measured by use of a thermistor. Calorimetric biosensors detect variations of heat during a biological reaction. 

An important point to emphasize is that some of the methods used to make the model catalysts, like EBL, are so expensive that they are unlikely to be used to make real catalysts, at least in a foreseeable future, except possibly in high-value products, like catalytic sensors. The merit of the technique is that it allows detailed scrutiny of what type of catalyst is best for a particular application. This insight can then be used to develop cheaper or better catalyst with the same end result. The latter translation is much easier if one knows exactly, e.g., what composition or structure one is aiming at. 

In the literature the two basic types of biosensors are also called binding sensors and catalytic sensors. 

In addition to these catalytic sensors, optical fibers also provide the prerequisites for the construction of affinity sensors. In the classical example, a glucose sensor [220], the lectin con-canavalin A, is covalently attached to the internal wall of a membrane stitched on the tip of the fiber, and it binds by affinity the fluorescein-labelled macromolecule dextran. The in-... 

Also for CO sensing, the present sensors are available only for the field of security not for environmental use because of the insufficient sensitivity and selectivity to monitor CO in the atmosphere. Examples of CO sensor which have been improved their sensitivity and selectivity are, for example, SnO semiconductor sensors operated under periodic temperature cycle[85-87], a electrochemical sensor using nafion membrane[88], a catalytic combustion sensor composed of catalysts and hydrophobic pol uner[89], a SnOj diode sensor doped with Pd[90] and an optical fiber catalytic sensor with Au/CogO as combustion catalyst[91]. 

The catalytic sensor is less sensitive to temperature and humidity effects, offers repeatable performance, and is relatively stable. However, it is susceptible to poisoning or inhibition from some gases, which may decrease its sensitivity or damage the sensor beyond recovery. 

Inorganic ions, drugs, nucleic acids, proteins, and even cells are successful examples of imprinting. In this way, affinity sensors, receptor sensors, and catalytic sensors based on MIPs have been explored. For affinity sensors, immunosensor-like devices were prepared by a 2D MIP technique with molecular imprinting on chemisorbed alkanethiol SAMs then after necessary procedures, vitamins Ki, K2, E, cholesterol, and adamantine could be detected by the strong electrochemical signals yielded. The sensors for nucleic acids, cholesterol, and catechol derivatives can be fabricated first by their adsorption as a template on the ITO surface and then by the treatment of the electrode with adsorbed template using trimethyl chlorosilane from the gas phase. 

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