Biological Signals

Machine Sensing, again an area we examined for product manufacturing process control.

Making Sense With Biology By Samuel Greengard  Commissioned by CACM Staff

November 11, 2021

Machine-based sensing has advanced remarkably in recent years, and now is used in an array of devices and systems. Yet for all the gains, silicon still can't match the innate capabilities of a moth or a dog. With hundreds of millions of years of evolution, a biological system wins every time.

Of course, scaling moth antennae and canine noses to check humans for diseases or spot ultra-low concentrations of hazardous particles is not possible. As a result, researchers are exploring ways to fuse biology and silicon into hybrid systems that deliver the best of both worlds.

Using a variety of techniques, including engineering bio-hybrid systems and tapping synthetic biology to grow artificial neurons that can interact with computing devices, they are opening the door to a brave new world.

"Living systems and synthetic systems can each do some things better than the other," says Thomas Daniel, a professor in the department of biology at the University of Washington in Seattle. "By combining them, it's possible to extend beyond the limitations of each."

Beyond Biology, .

Combining synthetic and living systems is not a new idea. Pacemakers, bionic implants, and other biomedical devices already bridge these two worlds. Now, however, instead of implanting technology inside a lifeform, researchers are exploring ways to place living cells inside silicon-based devices to create sophisticated bio-hybrid systems.

"Insects and certain animals can sense at about five orders of magnitude better than even the best synthetic device," Daniel explains. This makes it possible, for example, for trained dogs to detect COVID or cancer in humans. A moth and other insects can detect a variety of odors that can represent risks.

"The goal is to build devices that use biological sensing to address real-world issues," says Jennifer Talley, senior research biological scientist at the U.S. Air Force Research Lab. Biohybrid systems would detect viruses, diabetes, cancer, toxic chemicals, and other contaminates before they impact humans. They also would help first responders identify dangerous situations, including bombs and terrorist activity, before people are injured or killed.

In 2020, for example, a team from the University of Washington developed a drone, aptly named the Smellicopter, that uses insect antenna from a Manduca sexta hawkmoth to sense specific odors in the environment. Researchers attached the biological and silicon components by inserting tiny wires into the base and tip of the antenna and then using electrodes to measure electrical activity.

Not surprisingly, the use of biological components presents challenges. The antennae in the Smellicopter, for instance, remain biologically and chemically active for about four hours. As a result, biohybrid systems are typically limited to one-time use. This is fine for something like a virus test, but is a problem for more complex devices that would require constant refrigeration and replacement.

It also is a challenge to develop a single device that can handle multiple tasks. "Insects are typically hard-wired to 'smell' or 'see' certain things. You are essentially restricted to what they care about, whether it's food or a mate," Talley says.

Decoding the signals

All of this is leading researchers down a different path. Synthetic biology, including gene editing tools like CRISPR, now make it possible to design bio-hybrid systems. "You grow the sensor you want," Talley says. "By engineering neurons to accomplish a specific task, it becomes a lot easier to develop a functional system."