From bike reflector to virus detector

Caren B. Les, caren.les@photonics.com

You see them on spokes, sneakers, safety vests and signs, but now retroreflectors are taking on even more protective roles: detecting bioterrorism agents.

“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?” said project leader Dr. Richard Willson of the University of Houston in Texas. “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.”

So Willson and colleagues set out to create an all-in-one ultrasensitive instrument that can quickly tell first responders just which disease-causing microbe is responsible. This is where the retroreflectors come in.

Retroreflectors, by definition, reflectlight directly back to the source to produce a high level of brightness. The new ones are extremely tiny: 200 or more could fit on the head of pin, probably with room to spare. Dr. Paul Ruchhoeft, a UH researcher, made the tiny optics to fit onto a lab on a chip with microfluidic channels that process minute amounts of blood or other fluids, with no special sample preparation necessary.

The tiny retroreflectors shine brightly if there are no disease-causing viruses or bacteria in the sample; if a pathogen is present, the retroreflectors grow dark. The group has successfully detected the bacterium that causes Mediterranean spotted fever, and others are on the agenda.

“Right now, we have seven channels in our device,” said UH researcher Balakrishnan Raja. “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.”

The group’s focus now is on detecting norovirus, a rapidly spreading gastrointestinal bug known as “the cruise ship virus.” Their technology will involve retroreflector cubes that can be suspended in samples of fluid.

A version of the technology also could be used in health care settings to rapidly diagnose common infectious diseases, Willson said.

Scientists from the University of Texas Medical Branch and Sandia National Laboratories also worked on the project. The research was presented at a recent meeting of the American Chemical Society.