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Household cleaners using oxygen
may make blood removal too simple
Three common forensic tests foiled by hemoglobin’s fatigue
By Rachel Ehrenberg
CSI teams beware — a common household product cleans up blood thoroughly
enough to make it undetectable by three
of the most common forensic tests.
These “presumptive tests” are a quick-and-dirty way to identify important
stains — such as blood — at a crime scene,
says Walter Rowe of George Washington
University in Washington, D. C. The tests
rely on the blood protein hemoglobin’s
love of oxygen. But “oxy” cleaners appear
to drown hemoglobin in so much oxygen
that the protein has no love left for the
tests, scientists report in an upcoming
Naturwissenschaften.
While the research suggests a way for
immaculate killers to clean the scene,
most people who commit murder aren’t in
a frame of mind to think over which detergent to use to cover their tracks, Rowe
points out. “People committing violent
crimes often don’t have time to clean up;
they leave a lot of stuff behind.”
“Oxy” cleaners may make forensic tests,
like this luminol test for blood, ineffective.
Hemoglobin, a doughnut-shaped protein made of four globular subunits, carries oxygen from the lungs to the body’s
tissues. Each subunit has its own heme
group, a bit of iron bound in a protein
ring. It’s the iron that’s mad about oxygen. Existing forensic blood tests involve
swabbing the stain with hydrogen peroxide. If the stain is blood, the hemoglo-
bin tears the oxygen atoms away from
the hydrogen peroxide. With some of
the tests an indicator is added, such as
a chemical that changes color when it
reacts with the oxygen (thus the telltale
“pink” swab from crime scenes).
To investigate the possible doctoring
of evidence by the oxygen-rich cleaning
detergents, Fernando Verdú of the University of Valencia in Spain and his colleagues took samples of their own blood
and stained several fabrics, including a
soft cotton cloth, jeans and a towel. The
fabrics were washed with a product called
Neutrex that contains “active oxygen,”
or sodium percarbonate, which releases
hydrogen peroxide when dissolved in
water. The clothes were then soaked in
soapy, hot water for two hours. The team
also ran cold-water trials with and without oxygen-rich detergent.
Researchers then conducted three
different forensic tests on each cloth. All
tests were negative on stains washed in
warm water with the oxygen cleaner.
The sodium percarbonate “oxidizes
the daylights out of iron,” says Rowe. “It
probably is then not going to react with
anything.” And these cleaners probably
“tear up the protein molecule,” he says,
perhaps destroying DNA as well.
Design criteria
outline ways
to repel water, oil
Both liquids can bead up,
flow off textured surfaces
By Sid Perkins
A new set of design criteria could enable
engineers to invent and manufacture
surfaces that can repel almost all liquids,
even oily fluids long noted for their ability to foul water-repellent surfaces.
After designing and manufacturing
“omniphobic” surfaces that can repel
both water and oily liquids in 2007,
Gareth McKinley of MIT and his colleagues have come up with general rules
for creating the surfaces, the team reports
online November 10 in the Proceedings of
the National Academy of Sciences.
Besides the surface tension of the liquid and water repellency of the surface,
engineers should consider the size, shape
and spacing of the surface’s microscopic
features, McKinley says.
The new design criteria enable engineers to analyze existing surfaces or to
conceive new ones, says Robert Cohen
of MIT, a coauthor of the report.
When water-shedding surfaces become
contaminated with oily substances, the
surfaces usually lose their repellency,
says Marshall Ming of the University of
New Hampshire in Durham. “Successful
development of omniphobic surfaces is a
very exciting achievement” because of the
practical applications, such as self-cleaning paints or coatings for windows.
Coated with a fluorinated polymer, this
mat repels water (blue) and oil (red).
