Their report on progress in using these innovative
"retroreflectors" — the same technology that increases the night-time
visibility of traffic signs — was among almost 12 000 on the agenda of the
245th National Meeting & Exposition of the American Chemical Society, the
world's largest scientific society. More than 14 000 scientists and others are
expected for the meeting.
"Our goal is the development of an ultrasensitive,
all-in-one device that can quickly tell first-responders exactly which
disease-causing microbe has been used in a bioterrorism attack," said
Richard Willson, Ph.D., who leads the research. "In the most likely kind
of attack, large numbers of people would start getting sick with symptoms that
could be from multiple infectious agents. But which one? The availability of an
instrument capable of detecting several agents simultaneously would greatly
enhance our response to a possible bioterror attack or the emergence of a
disease not often seen here."
Willson's team is developing another version of the
technology intended for use in doctors' offices and clinics for rapid, on-site
diagnosis of common infectious diseases before patients leave. Eliminating the
need to wait for test results from an outside laboratory could allow patients
to get the right treatment sooner and recover sooner, Willson noted.
One of those tests focuses on detecting norovirus, the
dreaded "cruise ship virus," or "winter vomiting virus,"
which strikes more than 20 million people annually in the United States alone.
Norovirus was in the headlines last December when it struck 220 people on the
Queen Mary II.
Balakrishnan Raja, the member of Willson's team at the
University of Houston (UH) who presented the report, pointed out that retroreflectors
may be the most visually detectable devices ever made by humanity. They work on
the project with colleagues at UH, the University of Texas Medical Branch in
Galveston and the Sandia National Laboratories branch in Livermore, Calif. The
devices reflect light directly back to its source in a way that produces
extreme brightness. One version of retroreflection effect occurs when someone
shines a flashlight in a mirror. The reflection is so bright that looking at it
Although most people have never heard the term
"retroreflector," these devices are not new, Raja pointed out. The
Apollo 11 astronauts, for instance, left a laser-ranging retroreflector on the
moon during the first lunar landing mission in 1969. Scientists still use the
device to study the moon's orbit. And they are ubiquitous fixtures in road
signs, traffic lane markers and elsewhere in everyday life.
Willson's collaborator Paul Ruchhoeft of UH has developed a
way of making retroreflectors so small that more than 200 would fit inside the
period at the end of this sentence. The retroreflectors then become part of a
lab-on-a-chip, or a microfluidic device, with minute channels for processing
"microlitre"-scale amounts of blood or other fluids. A microlitre is
one-millionth of a litre (a litre is about one quart). A drop of water contains
about 50 microlitres.
When a sample of fluid that doesn't contain disease-causing
viruses or bacteria flows through those channels to the retroreflectors, they
shine brightly. A sample containing bacteria, however, makes portions of the
reflectors go dark, signaling a positive test result. Raja explained that the
change from bright to dark is one of several advantages of the retroreflector
technology, compared to existing ways of detecting disease-causing microbes. It
can be detected with simple optical devices, rather than expensive, complex
optics. The retroreflector technology also avoids the need to specially prepare
samples for analysis and is faster.
"Right now, we have seven channels in our device,"
Raja said. "So we can test for seven different infections at once, but we
could make more channels. That's one of our long-term goals — to multiplex the
device and detect many pathogens at once."
They have demonstrated clinically useful sensitivity on
samples containing Rickettsia conorii, a bioterrorism threat that causes
Mediterranean spotted fever, and others are on the agenda. A new version of the
technology involves retroreflector cubes that can be suspended in samples of
fluid. Willson's team initially will use it on norovirus with the goal of
developing a device that can raise a red flag on norovirus viral contamination
and prevent the disease's wildfire-like spread.