Reflectors on sneakers and bicycle fenders that help ensure the safety of runners and bikers at night are moving toward another role in detecting bioterrorism threats.
“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 “retroreflectors” 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,” Willson said. “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 said.
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), said retroreflectors may be the most visually detectable devices ever made. 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 hurts.
Although most people have never heard the term “retroreflector,” these devices are not new, Raja said. 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 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 “microliter”-scale amounts of blood or other fluids. A microliter is one-millionth of a liter (a liter is about one quart). A drop of water contains about 50 microliters.
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 said the change from bright to dark is one of several advantages of the retroreflector technology, compared to existing ways of detecting disease-causing microbes. A simple optical devices can detect it, 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 suspend 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.