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A well-recognized national security issue is the detection of chemicals and either biological agents or their components (i.e., toxins). For example, the inability to rapidly inspect mailed letters for the presence of anthrax spores provided a route for the targeting of the mail with infectious microorganisms in the United States in 2001. This demonstration has spurred development of more sophisticated, accurate, and rapid detection technologies. Aside from national security concerns, detection of chemical and biological compounds is important in a forensic investigation.

X-ray examination has long been of value in scanning luggage at airports. The same technology can be used locate objects hidden inside other objects. As well, newer x-ray technology enables the discrimination of organic from inorganic objects. Most of the x-ray beam is reflected back immediately upon encountering an object. Some of the radiation, however, passes through the object. By analyzing the beams that actually penetrate through an object, information on the object's composition is provided. Another version sends two different x rays of different wavelengths through an object. The different beams can distinguish between organic objects, such as food and paper, and inorganic objects.

A chemical detection technology known as gas chromatography has been sped into routine use in airports since the U.S. terrorist attacks of September 11, 2001. The different chemicals present on a cloth that is swiped over an object can be separated based on their different preference for the gas mixture that is pumped through the sample chamber. A target chemical (i.e., an explosive) is detected within seconds.

Chemical detection technologies have also been adapted for use "in the field," such as by United Nations inspectors deployed in Iraq beginning in November 2002, to the presence of missiles that were supposedly destroyed by the Iraqi government in the mid-1990s. These portable technologies are beginning to find their way into forensic use.

Sound can also be used to detect chemicals. For example, the acoustic wave sensor uses a quartz surface to convert incoming sound waves into electrical signals. Over a dozen different chemicals can be detected within seconds, even from biological sources. In another sound-based technique, called acoustic resonance, the pattern of vibrations when sound waves are sent inside an object can reveal whether the object is filled with a solid or a liquid, and even the type of chemical present.

Light is another means of chemical detection. The use of light is called spectroscopy. Mass spectroscopy determines the mass of proteins, which is important in determining the identity of the chemical or biological agent. Matrix-Assisted Laser Desorption/Ionization Mass Spectroscopy (MALDI-MS) can identify proteins that are unique to Bacillus anthracis (the cause of anthrax) and Yersinia pestis (the cause of plague). Raman spectroscopy measures the change in the wavelength of a light beam by the sample molecules. Optical spectroscopy measures the absorption of light by the chemical groups and the subsequent emission of light by the same groups as the identification method.

The ability to detect genetic sequences that are unique to certain bacteria (gene probing) has been exploited to develop genetically based microbial detection methods. The best example of gene probing is the polymerase chain reaction (PCR), which can enzymatically detect a target stretch of genetic material and rapidly amplify that region to detectable levels. Hand-held PCR detectors (i.e., Handheld Advanced Nucleic Acid Analyzer, or HANAA), used in the 2002–2003 inspections of Iraqi facilities by United Nations officials, are already being exploited in law enforcement.

Biological detection devices can monitor the surrounding air at regular intervals. Air is automatically drawn into the device and analyzed for target genetic sequences using the PCR technology. The results can be electronically relayed to a central database for analysis and shared with other law enforcement agencies.

Another biological technology utilizes antibodies that are produced in response to the presence of a specific microorganism. Tests are available that detect Bacillus anthracis, Clostridium botulinum, viruses (e.g., smallpox), and chemicals (e.g., ricin) in minutes.

Some older biological detection technologies still prove reliable in forensic analyses. Growth of micro-organisms on artificial food sources (media) produces populations called colonies. A medium can be selected that produces colonies that have a distinctive appearance and color. Gel electrophoresis separates differently sized pieces of genetic material or other microbial components (e.g., protein) into bands. The banding pattern can be used to identify the microorganism. Finally, chromatography separates compounds from one another based on their differing speed of movement through a gas or a liquid mixture.

SEE ALSO Aflatoxin; Bacterial biology; Bioterrorism; Chemical warfare.