Sensor Systems for Biological Agent Attacks Protecting Buildings and Military Bases (2005) / Chapter Skim
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8 Chemistry-Based Identification for Detect-to-Warn Applications
8 Chemistry-Based Identification for Detect-to-Warn Applications
Pages 130-148
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From page 130... ...
Although metabolites are typically not unique to any specific type of cell and are therefore not useful for identifying a particular class of microorganism, one exceptional small metabolite—dipicolinic acid—is diagnostic of some sporefomming microorganisms such as Bacillus anthracis, the bacterium that causes anthrax. · Nucleic acids.
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From page 131... ...
Other proteins may be common to multiple species of dangerous microorganisms and thus serve as useful flags for the presence of these organisms. Because of their relatively high cost and complexity, mass spectrometers are better suited to the identification of biological agents rather than their detection.
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From page 132... ...
Major classes of mass spectrometers that operate in this fashion are termed quadnupole mass spectrometers and ion-trap mass spectrometers. Several varieties of hybrid mass spectrometers exist.
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From page 133... ...
2001. Characterization of intact microorganisms by MALDI mass spectrometry Mass Spect Rev.
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From page 134... ...
Most of the current efforts in the use of mass spectrometry for bioagent detection are taking this approach. The currently fielded chemical biological mass spectrometer (CBMS)
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From page 135... ...
The pyrolysis fragmentation pattern is a function of many variables, and it has not been demonstrated that these signatures offer sufficient discrimination in a complex background to support a 1 0 3 false alarm rate. Challenges for Rapid, Simple-to-Use Mass Spectrometry identification Systems MALDI-TOF mass spectrometers are used routinely in laboratories to identify proteins.
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From page 136... ...
While mass spectrometry is certainly one of the mainstays of today s chemistry and biotechnology laboratories, current laboratory MALDI-TOF mass spectrometers do not come in small easy-to-use packages. They typically are benchtop- or floor-mounted systems at least the size of several three-drawer file cabinets.
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From page 137... ...
GAS- AND LIQUID-PHASE SEPARATIONS FOR PATHOGEN DETECTION While mass spectrometers are widely used in chemical laboratories, methods for separating molecules in flowing vapor or liquid streams are nearly ubiquitous. In these methods the sample streams flow through a column packed with material that interacts reversibly with molecules in the sample.
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From page 138... ...
Therefore, as with MALDI-MS idenbficabon of bioagents, work is needed to determine the suitability of this approach for the identification of bioagents in the presence of naturally occurring microorganisms and other aerosols found in the environments that are being protected. CHEMICAL SENSORS As discussed in the introduction, biological organisms and molecules display chemical characteristics that can be exploited to detect and identify them through a variety of chemical sensors.
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From page 139... ...
A complete listing of all transduction methods, chemically interactive surfaces, and combinations of sensor elements into arrays for chemical sensing is beyond the scope of this report. However, below is a brief overview of several common chemical sensor transduction principles and some important considerations for designing sensors for pathogen detection.
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From page 140... ...
For a reversible binding interaction, a sensor response will be observed when the analyte is present but will rapidly return to baseline when the analyte is removed. Many vapor-polymer interactions used in sensor arrays for vapor analysis are reversible within seconds under normal operating conditions.'Other interactions such as antibodyantigen binding or DNA hybridization require harsh conditions (e.g., high temperatures, low pH)
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From page 141... ...
This overview of chemical sensors only touches the surface regarding the multitude of chemically interactive films, chemical transducers, sensor arrays, and other considerations that must be taken into account when developing chemical sensor systems. In order to develop effective chemical sensors, it is critical to first understand the operating requirements and sample type, and to consider the complete system, from sample acquisition through detection and data analysis, since these requirements can dramatically change the selection of the chemical sensor system and sensing strategy.
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From page 142... ...
The use of chemical sensors for semiselective pathogen detection is an area that has not been extensively investigated. Below are a few examples of chemical sensors that are being developed.
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From page 143... ...
However, additional research and development would be required in the areas of microfluidics, reagent storage, and optical sensor systems to develop a small, integrated sensor system that could automatically analyze liquid samples generated from an aerosol sampler. As with the other dpa detection methods discussed previously in this chapter, this semiselectve assay will only detect the presence of spores, so for general pathogen detection, strategies must be developed to combine this assay with additional sensors that detect other pathogens of concem.
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From page 144... ...
Because many types of planar chemical sensors can be miniaturized, strengthened, and Cheapened, this general approach, with further development, has the potential to be used as a biological smoke detector that could be distributed throughout facilities. In one approach, scientists are developing a pathogen detection system that includes fluorescent dyes immobilized onto a quartz substrate or optical fiber.39 The system is designed so that the fluorescence signal is enhanced when analytes of interest bind to fluorescent dye molecules that are immobilized onto the sensor surface.
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From page 145... ...
The DNA dyes will stain all nucleic acids, and the protein dye binds electrostatically to COOH and OH groups, so complete characterization of the sensors in environmental samples will be required to detemmine the utility of these semiselective sensors. The detection limit for DNA-based detection of organisms is currently 1,000 organisms bound to the sensor surface,44 and the detection limit for cholera toxin is currently 120 nanomoles.45 Encouraging data have also been obtained that indicate that binding of the fluorescent dye molecules to the many identical binding sites on dendrimers can increase the optical signal and improve the stability of a fluorescent dye used for DNA staining.
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From page 146... ...
The response times of vapor sensor arrays are on the order of seconds, and the vapor interactions are reversible, so that rapid air monitoring can be done over extended periods of time with a single sensor arTay. A nugged vapor sensor system will have to be designed to prefilter particles that will foul the sensor surface, or the surface will have to be renewed periodically when surface fouling occurs.
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From page 147... ...
These activities should be pursued using the best-performing laboratory mass spectrometers. To the extent that recent MALDI mass spectrometry actvibes show improved detection perfommance and discrimination in the presence of interfering backgrounds, spectrometers in this class may deserve a higher priority.
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From page 148... ...
. Recommendation 8-3: Common guidelines for reporting of the testing and perfommance of pathogen detection systems should be developed.
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