Biodetectors

█ JUDYTH SASSOON

Biodetectors are analytical devices that combine the precision and selectivity of biological systems with the processing power of microelectronics. Biodetectors act as powerful analytical tools in medicine, environmental diagnostics, and food industries, as well as forensic analysis and counterterrorism. Biodetectors usually consist of a biological recognition system, typically enzymes or binding proteins immobilized on a surface acting as a physicochemical transducer. One typical example of a biodetector is the immunosensor, which uses antibodies as the biorecognition system. In addition to enzymes and antibodies, the recognition systems can consist of nucleic acids, whole bacteria and single cell organisms and even tissues of higher organisms. Specific interactions between the target molecule or analyte and the complementary biorecognition layer produce a detectable physico-chemical change, which can then be measured by the detector. The detection system can take many forms depending upon the parameters being measured. Electrochemical, optical, mass or thermal changes are the most common parameters providing both qualitative or quantitative data.

The sensitivity of biodetectors allows them to be of considerable use as early detection systems against chemical or biological attacks. They are employed to monitor the environment and can respond to low concentrations of any harmful substances that may be present. Biowarfare agents are frequently colourless and odourless and can sometimes take days to cause symptoms. Early detection of these agents is particularly important as they can trigger symptoms, such as fever or nausea that might be initially mistaken for relatively benign conditions like influenza. Biological agents become weapons of mass destruction when they are disseminated through the air as breathable aerosols. Droplets containing the agents can travel through the air over long distances. A healthy human being breathes on average six litres of air per minute and some of the most lethal pathogens are capable of causing disease if as little as ten organisms are inhaled. To be useful as an early warning device, a biodetector must therefore, have a sensitivity that can detect fewer than about two organisms per litre of air.

The biodetectors now under development for use in counterterrorism fall into three broad categories: biochemical systems detecting a DNA sequence or protein unique to the bioagent through interaction with a test molecule; tissue-based systems, in which a bioagent or toxic chemical affect living mammalian cells, causing them to undergo some measurable response; and chemical mass spectrometry systems, which break samples down into their chemical components whose weights are then compared to those of known biological or chemical agents.

In recent years, researchers have been sequencing the DNA of a number of potential biowarfare agents in an effort to make them available for DNA based biodetector technologies. A microarray of gel-immobilized, fluorescence-labeled nucleic acids has been developed by Argonne National Laboratory. One application of array systems would be to develop a "bacillus microchip" for detecting Bacillus anthracis (the anthrax agent). It would distinguish B. anthracis from other related bacteria, such as B. thuringiensis, B. subtilis, and B. cereus and also indicate whether the organism is alive or dead by detecting DNA when there are no RNA matches.

A number of new, fast, reliable, and portable DNA detection devices have been developed that can prepare and test samples within a very short time. Devices consisting of cell disruptors, capable of breaking bacterial spores and extracting DNA, which is then used to identify the species of organism, are being tried. Some companies have incorporated an automated sample preparation scheme and coupled it with a microfluidic "lab on a chip" device for detecting microorganisms on the basis of their DNA sequence. The system is said to reduce a laboratory preparation procedure that can take six hours to just 30 minutes. The chip contains tiny channels, valves, and chambers through which milliliters of sample can be pumped and concentrated into a microliter volume. Any bacterial cells are broken ultrasonically and their DNA is extracted, amplified by PCR (polymerase chain reaction) and sequenced.

A DNA-based biochip designed by Northwestern University detects DNA sequences that are specific for pathogenic microorganisms. The chip initially contains very short single strands of DNA between two small electrodes. The DNA strands are complementary to DNA sequences from a specific pathogen. When DNA from that pathogen comes into contact with the chip, it hybridizes with the DNA on the chip. To detect the hybridization, further pieces of DNA are added to the system and these are complementary to the sections of pathogen DNA that have not hybridized. The additional DNA pieces contain gold particles that, on successful hybridization, form a bridge of conducting metal linking the two electrodes. The bridge completes an electrical circuit which raises an alarm.

█ FURTHER READING:

PERIODICALS:

Behnisc, P.A. "Biodetectors in Environmental Chemistry: Are We at a Turning Point?" Environ Int 27(2001):441–2.

Casagrande, R. "Technology against Terror." Scientific American. 287 (2002):59–65.

"Early Warning Technology." Med Device Technol 13 (2002): 70–2.

SEE ALSO

Biological and Toxin Weapons Convention
Biological Warfare
Biological Warfare, Advanced Diagnostics
Biological Weapons, Genetic Identification
Biosensor Technologies
Chemistry: Applications in Espionage, Intelligence, and Security Issues
Forensic Science
Isotopic Analysis
Microbiology: Applications to Espionage, Intelligence and Security
Molecular Biology: Applications to Espionage, Intelligence and Security Issues