Skip to Content

Blue Is for Biohazard

A novel sensor uses liquid crystals to detect environmental contamination.
August 27, 2001

A chemical sensor that changes color in the presence of toxins may one day save lives on the battlefield and in hazardous industries, report researchers in the August 17 issue of Science magazine.

The sensor, developed at the University of Wisconsin, uses liquid crystals to detect environmental contaminants.

“It’s a direct visual indication, and it requires no electric power,” Nicholas Abbott, the study’s lead investigator, told technologyreview.com. “It’s sufficiently simple that it might find use in personal monitoring.”

Get in the Groove

Abbott’s device consists of three components: a bottom layer of gold patterned with nanoscale grooves, receptor molecules embedded in that layer, and a top layer of liquid crystals attached to the receptors by a loose hydrogen bond. This bond controls the liquid crystals’ orientation, which determines their appearance to the human eye.

When the sensor encounters a target compound (a toxic gas, for example), that compound forms a strong bond with the receptor molecules, breaking the liquid crystals’ weak hydrogen bonds. The suddenly free liquid crystals orient themselves along the grooves in the gold layer, which changes the sensor’s appearance. When the target compound is no longer present, the liquid crystals reattach to the receptors and the sensor’s appearance returns to normal.

In their experiment, Abbott and his colleagues used carboxylic acid groups for receptors. The acid groups formed a weak bond with the liquid crystal layer, but a strong bond with the poisonous target compound, hexylamine.

This approach, called competitive binding, helps the device avoid false positives. The sensor distinguished the target compound from alcohol, hexanes, water vapor and other chemicals. Some experimental detectors, Abbott says, have an especially hard time distinguishing their targets from water, a shortcoming that limits them to the laboratory.

“The Abbott system is very exciting work for detection of vapor phase (gas) toxins,” says Jerome Workman Jr., a senior research fellow at Kimberly-Clark and an expert in analytic devices.

Fast, Cheap and Under Control

Today, the most common field instrument for detecting environmental toxins is the portable gas chromatograph, which costs thousands of dollars and weighs upwards of 50 pounds, although devices that detect only one or two compounds may weigh as little as ten or fifteen pounds, says Eric Anderson of Buck Scientific, a manufacturer of analytical instruments.

Abbott says his detector is not only cheaper to manufacture, but more portable and easier to use: a person could wear the device as a color-changing badge, similar to those that measure radiation exposure. The badge could feature receptors for many different compounds, arranged in an array or in patterns. “The pattern that develops could be a letter or a word, so it could be understood by a non-technical person,” Abbott says.

Although the device currently detects only gaseous compounds, Abbott hopes to develop a version that works with fluids. He is also working to develop liquid-crystal detectors for complicated biological targets, including viruses and bacteria, and reports some success already detecting protein binding.

“This is a real frontier issue, detecting environmental contaminants of all types,” says Bruce Rittman, professor of environmental engineering at Northwestern University. “Getting rapid information is the weak link now; some of this takes a really long time. If you can do this, it’s a fantastic benefit.”

Keep Reading

Most Popular

still from Embodied Intelligence video
still from Embodied Intelligence video

These weird virtual creatures evolve their bodies to solve problems

They show how intelligence and body plans are closely linked—and could unlock AI for robots.

pig kidney transplant surgery
pig kidney transplant surgery

Surgeons have successfully tested a pig’s kidney in a human patient

The test, in a brain-dead patient, was very short but represents a milestone in the long quest to use animal organs in human transplants.

panpsychism concept
panpsychism concept

Is everything in the world a little bit conscious?

The idea that consciousness is widespread is attractive to many for intellectual and, perhaps, also emotional
reasons. But can it be tested? Surprisingly, perhaps it can.

We reviewed three at-home covid tests. The results were mixed.

Over-the-counter coronavirus tests are finally available in the US. Some are more accurate and easier to use than others.

Stay connected

Illustration by Rose WongIllustration by Rose Wong

Get the latest updates from
MIT Technology Review

Discover special offers, top stories, upcoming events, and more.

Thank you for submitting your email!

Explore more newsletters

It looks like something went wrong.

We’re having trouble saving your preferences. Try refreshing this page and updating them one more time. If you continue to get this message, reach out to us at customer-service@technologyreview.com with a list of newsletters you’d like to receive.