Strings of DNA 311.
(photo credit: Wikipedia images)
At crime scenes, DNA from a suspect, the victim and other people are often
mixed, thus confusing forensic scientists. Now the Hebrew University’s
technology transfer company Yissum has introduced a method for forensic
profiling even when the DNA is not “pure.”
Forensic DNA science has
advanced significantly in the past decade, and today constitutes the mainstay of
forensic science. All serious crime scenes are routinely inspected for DNA
evidence, and many cases are solved by matching the DNA found to that of a
suspect. But often a crime scene will contain complex DNA mixtures – usually
from more than two individuals – making the detection of a particular DNA
profile challenging. In such cases, current police practices overlook valuable
information that may aid in solving crimes.
The new technique, developed
by HU geneticist Prof. Ariel Darvasi in collaboration with Lev Voskoboinik from
the Forensic Biology Laboratory of the Israel Police (as part of his MSc thesis)
consists of checking the DNA mixture and the suspected individual’s DNA for
1,000 to 3,000 single “letter” changes (polymorphisms) that are relatively rare
in a given population. Their work was recently published in Forensic Science
“DNA profiling has become an indispensable tool
in crime investigations, and is used both to convict and acquit. It is therefore
of great importance that crime investigators be able to determine whether a
suspect is indeed connected to the crime scene,” says Yissum CEO Yaacov Michlin.
“The novel DNA profiling method will enable police to investigate even complex
crime scenes containing DNA from multiple individuals and discern with high
reliability the presence or absence of DNA from a specific
Human DNA consists of long chains comprising various
combinations of four small molecules, referred to as A, G, C and T. Forensic DNA
analysis is based on the fact that the exact DNA “script” of each human is
unique. The human genome, our DNA, comprises three billion letters, 99.9% of
which are identical in any two random individuals. Yet the remaining 0.1%,
corresponding to about 30 million possible changes arranged in various
combinations, enables each of us to carry our own DNA “barcode.” Thus, in a
particular position along the DNA chain, one person will have the letter A,
whereas another will carry the letter G.
Current DNA profiling methods
check a few such “polymorphic” sites, and if they all match a suspect’s DNA
exactly, one can establish with extremely high certainty that the DNA found at
the scene belongs to that suspect.
But if the DNA found is a mixture from
more than two individuals – which is often the case – current DNA analysis
methods are inefficient. The invention can establish if a suspect’s DNA is
present in a DNA mixture from up to 10 individuals.
involves analyzing the DNA mixture for 1,000 to 3,000 polymorphic sites where
DNA letter changes are rare (i.e. found only in about 5% to 10% of the
population). Thus, a suspect will carry about 100 to 200 of these rare letter
changes. If the DNA mixture collected at the crime scene does not include the
suspect’s DNA, there’s almost no chance that all of his/her 100 to 200 specific
and rare letters will be present. On the other hand, if all these rare
polymorphisms are present, then the only logical explanation is that the mixture
included the suspect’s DNA.NANOSIZE SENSORS
tell the airbag in your car to inflate, or rotate your iPhone screen to match
your position on the couch. Now a research group at Tel Aviv University’s
engineering faculty is making the technology even more useful. Prof. Yael
Hanein, Dr. Slava Krylov and their doctoral student Assaf Ya’akobovitz have set
out to make sensors for microelectromechanical systems (MEMS) much more
sensitive and reliable than they are today. And they’re shrinking their work to
More sensitive sensors means more thrilling videogames,
better-functioning prosthetic limbs, cars that can detect collisions and
dangerous turns before they occur, and – in the defense industry – missiles that
can reach a target far more precisely.
Able to sense the movement of
individual atoms, the researchers’ new MEMS sensing device uses small carbon
tubes about one-billionth of a meter long. Creating these tiny tubes using a
process involving methane gas and a furnace, Hanein has developed a method that
enables the atoms to “arrange themselves” on the surface of a silicon chip and
accurately sense tiny movements and changes in gravity.
In the device the
team developed, a nanometer-scale tube is added onto much larger
micrometer-scale MEMS devices.
Small deformities in the crystal structure
of the tubes register a change in the movement of the nano object, and deliver
the amplitude of the movement through an electrical impulse. “It’s such a tiny
thing,” she says. “But at our resolution, we are able to feel the motion of
objects as small as a few atoms in size.
Originally developed mainly for
the car industry, miniature sensors are all around us, she adds. “We’ve been
able to fabricate a device where the nano structures are put onto a big surface
– and they can be arranged in a process that doesn’t require human intervention,
so they’re easier to manufacture.
We can then drive these nano-sensing
tubes to wherever we need them to go, which could be very convenient and
costeffective across a broad spectrum of industries.”