A soldier walks through a building in a war zone. Suddenly, an alarm begins going off in his pocket. He pulls out a sensor about the size of a deck of cards. Sensors react to specific substances or changes in their environment.

This sensor has detected anthrax.

Anthrax is a microorganism that can cause serious illness, even death. It has been used as a biological weapon, also known as a bioagent.

The soldier alerts the rest of his patrol. They evacuate the building. This sensor doesn’t exist—yet. But ASU researchers are working to make it a reality.

“The state of the art biosensor is pretty poor,” says Stephen Goodnick, a professor of electrical engineering. “You don’t want to empty the New York City subway system based on a biosensor that’s only 30 percent accurate.”

A very good system for detecting bioagents already exists. Gas chromatography can achieve 99 percent accuracy. But gas chromatography is expensive and must be performed in a lab.

Portable and cheap bioagent sensors also exist. But they have a big problem. They sometimes sound the alarm when they come into contact with substances that aren’t dangerous. This is called a false positive.

False positives are expensive and disruptive. People have to be evacuated. Special workers are called in to contain and clean up the bioagent. If there’s no real danger, then people get annoyed.

“Our sensors have the best false positive rates because they’re based on biology and a very specific type of binding,” says Trevor Thornton. Thornton is also a professor of electrical engineering.

ASU is working with labs at Rush Medical College in Chicago and six other universities. The researchers have created a sensor that combines a tiny silicon chip with a cell membrane.

A membrane made of fat molecules forms the boundary of all cells. A cell membrane is like the walls of a house. The walls keep some stuff inside and other things outside. Getting into the house requires a door. Cars enter through the garage door. People walk in through the front door. Pets enter through a doggie door. Proteins in the cell membrane, called an ion channel, act like doors that only allow certain materials to enter and exit.

The heart of the sensor is a silicon chip like the ones found in computers and other electronic devices. In the chip is a tiny hole 100 microns across, the width of a human hair. A very thin layer of Teflon coats the chip. Teflon is a plastic often used in nonstick coatings on frying pans and cookie sheets.

Across the hole stretches a membrane, kind of like the ones around cells. Cell membranes normally contain many different ion channels. The membranes in the sensor contain many copies of the same ion channel.

The chip is surrounded by a solution of water and salts. Electrodes on the silicon measure the electric current through the ion channels. The current is very small, so the electronics are extremely sensitive. When a molecule of a bioagent enters the solution surrounding the chip, the current across the ion channels changes. The electrodes detect this change and sound the alarm.

“It’s amazing that we are able to measure a single protein,” says Seth Wilk, a postdoctoral research associate. “I like being able to see a device actually do what we planned for it to do.”

The first part of the research was to figure out if the sensor could be built at all. The researchers have proved that it can be. Now they are creating a model with the specific characteristics they want. The sensor should fit in a pocket. It must work for at least 90 days. And it should contain at least a dozen different membranes. Each membrane will contain a different ion channel that detects a different bioagent.

The researchers will test their system against chemicals that are similar to bioagents but not as dangerous. They will also make sure that the sensor doesn’t give false positives. A lot of work still needs to be done before one of their sensors ends up in a soldier’s pocket. But in the future, it could end up saving lives.