ENCYCLOPEDIA OF Espionage, Intelligence, and Security Volume ...

DNA Sequences, UniqueHybridization-based instruments. The great advantage ofhybridization-based instruments is the fact that they donot require any DNA amplification, are highly sensitiveand give rapid results.Scientists in industry are currently producing instrumentsthat are based on measuring electrical conductivity.One is known as the eSensor. The system consists ofbioelectronic chips, reader, and special software. The chipscontain capture probes and signaling probes. After aninteraction with a target sequence, signaling probes induceelectric current, which is detected and interpreted bythe sensor’s software. This instrument can perform anumber of assays simultaneously. A second instrument isdirectly based on the technology from the NorthwesternUniversity group, using a method of conductivity detectionthat was modified to amplify the signal from goldparticles by using a photographic developer solution tocoat the gold particles. Although this instrument currentlyrequires a large space, work is underway to design a handhelddevice.One company has licensed a Strand DisplacementAmplification (SDA) method, and has devised an electricalmethod of binding DNA to silicon chips and performinghybridization. SDA oligonucleotides (probes) are localizedto spots on the chip by charge and immobilized on thesurface by chemical reaction. The sample is then added tothe chip and by applying an electric current, the binding oftest to the probes is highly accelerated (one to threeminutes). By reversing the charge, unbound moleculesare removed and only perfect matches remain. The entireprocess takes about 15 minutes. Chips for identifyingpathogens such as the bacteria responsible for anthrax areunder development.PCR-based instruments. The newest technologies inpolymerase chain reaction (PCR)-based instruments involveinstrument miniaturization and methods for handlingand detecting multiple pathogens in multiple samples.The ability to prepare clean PCR templates in a field isoften difficult or limited. However, the presence of variouschemicals can inhibit the amplification, giving false negativeresults and, in the case of an attempt to identify abiological threat, possibly endanger people’s lives. As aresult, a number of companies have started to offer samplepreparation units with their PCR instruments.The advanced nucleic acid analyzer (ANAA), developedin 1997, was the first DNA recognition instrumentdesigned for work in the field. It was portable, but stilllarge and was superseded by a hand-held ANAA (HANAA).The major differences between the various instrumentsare in the proprietary heating and cooling systems,detection optics, and sample preparation and handling, aswell as size. Speed of most of these instruments is similarwith the typical sample analysis taking 7–20 minutes.A different technology, but still PCR-based, uses ahigh-performance liquid chromatography to separate thePCR products and identify mutations. The advantage ofthe system is that it can detect mutations in any genes thatcould have been altered for designing biological weapons,thus, potentially complementing any other detectionmethods.Application of DNA recognition instruments. DNA recognitioninstruments are likely to be used in general monitoring ofthe environment, investigation of suspicious objects, andin diagnostics. In all of these applications, detection mustbe rapid and accurate in order to introduce preventionmeasures or rapid treatment. Ease of use and result interpretationare important, as in majority of cases, users willbe people with minimal laboratory training.As of 2003, the majority of these advanced DNArecognition instruments were or are undergoing final testingin the field. They are able to cope with samples ofwater, food, and various clinical samples to detect anenvironmental contamination or identify a pathogen causingunusual symptoms in humans or domestic animals.❚ FURTHER READING:PERIODICALS:Belgrader, P., W. Bennet, D. Hadley, et al.”PCR Detectionof Bacteria in Seven Minutes.“ Science no. 5413: 449–450.Cao, Y. W. C., R. Jin, C. A. Mirkin. ” Nanoparticles withRaman Spectroscopic Fingerprints for DNA and RNAdetection.“ Science no. 5586 (2002): 1536–1540.Park, S. J, T. A. Taton, and C. A. Mirkin. ”Array-BasedElectrical Detection of DNA with Nanoparticle Probes.“Science no. 5559 (2002): 1503–1506.SEE ALSOBiosensor TechnologiesBioterrorism, Protective MeasuresDNA Sequences, UniqueDNA Sequences, Unique❚ AGNIESZKA LICHANSKADeoxyribonucleic acid (DNA) contains genetic informationof an organism that is unique for each organism. Theentire cellular DNA of any organism, bacteria, plant oranimal is known as its genome, as is the entire geneticmaterial of a virus. A DNA sequence is considered to beunique if it is present in only one copy in a haploidgenome. A haploid genome contains only a single copy ofeach chromosome. In humans, for example, a haploidnumber of chromosomes is 23. However, not all of theDNA contained in the genome is considered as unique;there are also various repetitive sequences present.340 Encyclopedia of Espionage, Intelligence, and Security