Imagine prowlers broke into your company warehouse over the weekend. The alarm sounded, but the devious blaggards got away with the goods before the police arrived. Your security cameras caught only dim, shadowy images of the intruders, not clearly enough for positive identification. DNA tagging could change that.
Normally, tracking a criminal using DNA requires, at a minimum, that the perpetrator leaves behind a DNA sample in some form or other. As they are not often so accommodating, the role of DNA in crime busting, while significant, has its limits.
Applied DNA Sciences (ADNAS) has developed a new approach to solve crimes using DNA tagging. The difference is that instead of tagging the objects being stolen, they tag the pilferer with DNA. While this has been tried before by applying the DNA to a fleeing criminal with a gun, ADNAS has adopted a more subtle approach.
For years banks have rigged bags of money with exploding dye packs, which mark the outlaw and the stash. The ADNAS system takes advantage of that basic concept, but implements it differently, so that a thief can be tagged without having a clue that their career will be cut short.
DNA Fog is an airborne suspension of artificial DNA molecules with a known but biologically inert sequence. The DNA molecules (Applied DNA's SigNature DNA) are artificially constructed, so that a strand of DNA with 20 base pairs can have over a trillion unique combinations. A security system could use one sequence per location, one sequence for each area within the location, or even use RFID tags to instruct a sophisticated spraying device to spray a unique DNA signature for each item stolen.
Once released, DNA molecules attach onto a malefactor's clothing, shoes, hair, and skin, as well as the objects stolen. This is rather like putting exploding dye packs in bags of money, save that the perpetrator has no idea that he has been marked.
It is surprisingly hard to scrub all the DNA off of one's body, clothing, shoes and tools. Regardless of what conventional cleaning methods a thief chooses, they will be easily detected to have been at the scene of the crime at the time it was committed for a period of at least two weeks, and potentially for years.
Should a guilty suspect be arrested, police would swab them and their clothes (and probably their apartment and car), then read the DNA samples using the polymerase chain reaction, which amplifies the genetic material from the sample to the point that it can be identified. The video below illustrates this reaction.
Amplifying makes the DNA samples easier to detect and analyze, and the overall process is simple and cheap enough that it can be done by non-specialists.
Can DNA Fog be defeated? There are couple of possibilities here. The low-tech approach is to wear an overall Tyvek suit with a diving mask. A higher-tech method is to swamp the DNA Fog system, perhaps by bathing with a body shampoo that contains millions of false DNA fragments. This would make it difficult for investigators to find the right sequence. It becomes a needle in a haystack problem, except the needle is also made of hay.
Applied DNA Sciences has recently entered into a two-way exclusive arrangement with SmokeCloak, a Danish security firm that manufactures security fog generators that can fill a room or a warehouse at up to 1600 cubic meters per minute, which is a depth of 1.5 feet per acre each minute.
Source: Applied DNA Sciences via Discovery.com
I can think of a few other reasons its usefulness is limited. For example, if the DNA is really that difficult to completely remove, a corollary is that someone who is sprayed is going to be shedding it all over everything in their vicinity for quite a while, including other people.
It would not stand up as a single definitive piece of evidence but if a suspect and his family and friends had the tag they would ask which of these people had no alibi, a criminal record, a stolen item in his possession etc.
Eventually they could replace the DNA with dust size RFID chips. But this is a good step towards that sort of system.
The student would have told you that "bathing" in "false" DNA fragments would not defeat this system.
It is easy to find one specific strand of DNA among trillions and trillions of other ones, because of the way DNA works. If you know the specific sequence (and we do in this case because it is designed to be unique), then you can target and amplify that sequence and only that sequence using PCR.
PCR was developed by Kary Mullis, earning him the Nobel Prize in chemistry. Anything involving detection of DNA samples uses PCR. http://en.wikipedia.org/wiki/PCR