Expanding the Vision of Sensor Materials (1995) / Chapter Skim
Currently Skimming:
CHAPTER 6: CHEMICAL SENSORS
CHAPTER 6: CHEMICAL SENSORS
Pages 73-88
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 73... ...
The capability of chemical sensing technology is substantial and has grown steadily over the past several decades, but it has been outpacec3 by the needs and diversity of chemical measurements. Materials limitations are prominent among the existing limitations of chemical sensors.
|
From page 74... ...
The discussion of chemical sensor types is divided into two sections: · direct-reading, selective sensors (e.g., electrochemical sensors, optical fibers) ; and · sensors that use a preliminary chromatographic or electrophoretic sample separation step followed by sensitive, but not necessarily selective, detection.
|
From page 76... ...
SENSORS WITH SAMPLE SEPARATION Chromatographic or electrophoretic separation in chemical analysis has classically not been considered to be a "chemical sensor." However, the difficult analyte selectivity issue of direct-reading sensors can be avoided by using a chromatographic or capillary electrophoretic format. In this case, a mixture of analyses flowing under pressure, or under an electrical gradient, are separated as a result of localized environmental interactions which can then be cletected as they flow sequentially past the detector (sensor)
|
From page 77... ...
Improvements in inexpensive mass ana Tyzers with a truly portable format have the potential to revolutionize approaches to chemical sensing based on combinations with high-speed gas or liquid chromatography or with capillary electrophoresis. Miniaturization would almost certainly degrade the mass analyzer resolution, but even a [Low-resolution capacity would find many applications and would offer benefits in multiplexing.
|
From page 78... ...
on-site monitoring of chemical warfare agents, precursors, and degradation products under the Chemical Weapons Convention.5 These examples serve to illustrate differences in clesign and selection of chemical sensors and existing materials constraints within the general 78 context of toxic chemical monitoring. Many of these ideas and technologies for improved chemical sensing can be applied to other types of environmental momtor~ng.
|
From page 79... ...
However, two additional factors significantly influence the development of chemical sensors for environmental monitoring: the requirement for a complex monitoring strategy covering the transport of toxic chemicals from source to human exposure and the influence of regulatory requirements. The general pathways for transport of toxic materials from their sources to produce human exposure, with potential ensuing absorption, metabolism, and adverse health effects, are summarized in Figure 6-2.
|
From page 80... ...
Thus sensing of environmental chemicals is a substantial, complex challenge that dictates several key requirements that affect sensor technology: · The difficulties in attaining adequate selectivity of sensor response to the desired toxic analyte apply to environmental monitoring as well as to other types of chemical sensing. · Environmental sensing requirements further justify the emphasis on miniaturization of chemical sensors, particularly for use in mass-producible formats.
|
From page 81... ...
will be madeb In the absence of suitable commercial products, up to $10M will be spent over 5 years to develop sensor system Manufacturability Not applicable Life cycle Total number of units too small for problem RELIABILITY Lifetime 2 years, multiuse on inspection tours, hundreds of cycles Calibration Once per month or before each country tours ACQUISITION (data) Discrete, with about 10 seconds between readings; internal data storage, possibly with encryption, with data sent to a microcomputer later IMPLEMENTATION Scale Array or alternative detector scheme for measurement over a large area Format Chemical sensor array or other detector scheme will feed information to microprocessors Mode Hand held unit with small pump for sampling vapor TRANSDUCTION No specification made TRANSDUCTION MODE No specification made MEASUREMENT SCALE No specification made aA detailed list of compounds and required sensitivities is not yet available.
|
From page 82... ...
The matrix shown in Table 6-3 summarizes the results of comparing specification requirements anct attributes of candidate sensing technologies using the descriptors. Anticipated problems in meeting specification requirements with available technologies have been marked "X," and particularly desirable features of the candidate systems have been marked with a "+." Use of the descriptor terminology and approach developed in Chapter 2 is extremely useful in conducting a comparative evaluation of different technologies.
|
From page 83... ...
Open access to specialized equipment and facilities, such as those required for lithographic patterning, can be crucially important to foster interest and progress as applications to specific practical analytical and chemical sensing measurements start to appear. As previously mentioned, the most important materials-related opportunities to improve directreading chemical sensors involve the choice of materials employed to elicit stable selectivity of interaction with the target analyte.
|
From page 84... ...
The detection of chemical weapons is a specific type of environmental sensing. The following materials areas have been identified by the committee as important in developing candidate sensor technologies to meet requirements for chemical weapons detection: · fiberoptic coatings with improved chemical selectivity, for example, selective analyte absorption (a polysiloxane film has been shown to re
|
From page 85... ...
; · new membranes and electrode coatings to obtain improved chemical selectivity with electrochemical sensors; and · chemically selective films that undergo changes in mechanical and electrical properties following analyte sorption (SAW devices)
|
From page 86... ...
1992. Selective surface acoustic wave-based organophosponate chemical sensor employing a self-assembled composite monolayer: A new paradigm for sensor design.
|
From page 87... ...
6. Appendix F describes in more detail several chemical sensor platforms based on this technology.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.