A new kind of sensor: Why this chemical detector doesn't need a battery

Soon, sensors might be able to sniff out explosives and chemicals in the human body - without a battery. All the sensors need is a little charge from nanowires.
Written by Boonsri Dickinson, Contributing Editor on

In some ways, sensors haven't changed much over the years. Their unassuming presence, allows them to secretly lurk in the distance — and detect unusual substances in the environment.

In a 1962 story printed in the Eugene Register-Guard, a cutting edge sensor network was described as: "Each detector is housed in a white aluminum cylinder about 12 inches high and 9 inches in diameter." That seems pretty big, considering today's nano-sized standards.

No doubt, sensors keep shrinking: Sensors can be designed to detect molecules inside the human body (viruses and proteins) and substances in battlefields (bombs).

You'd think that by now, senors would be everywhere - monitoring chemicals in the body and the environment. But there's one thing holding them back: battery power.

Conventional solid state sensors require a battery. Without a battery pack, the device wouldn't be able to send electrical signals that are important in identifying the mysterious chemicals. The battery is much larger than the sensor itself.

Lawrence Livermore researchers want to change the battery-sensor dilemma: Enter a battery-less sensor that uses silicon nanowires to get a charge. The chemical detector can also act like a battery, and give neighboring sensors extra energy.

"We've created a new generation of sensors, in terms of the sensitivity and in terms of concept. The main breakthrough is that it doesn't require a battery," Livermore researcher Yinmin (Morris) Wang said.

Size does matter: Smaller is better.

"The key is we can use the nanosensor to convert energy from the environment and can even use it as a battery," Wang said.

This chemical detector gets a charge when electrical voltages are produced on semiconductor nanowires in solution.  Not only is it cheap, it can sense chemicals pretty rapidly.

It's this rapid response that makes this next generation of battery-less sensors ideal for war zones applications.

Granted, the actual sensor is only about 2 millimeters. In the lab, the sensor performed well, after it was tested against a range of organic solvents and voltages. The researchers realized the sensor responds differently to each solvent and produces a chemical signature unique to each.

Think of it like a DNA type-of test, a tool for environmental detectives. The ends of the nanowire act like a battery in solution. The huge advantage? Electrical signals are generated instantaneously though the nanowire charge.

"We already tested the detector on the complex molecules related to explosives for biosecurity detection at airports and in the battlefield. In the body, complex proteins and viruses will give you different signals. Each particular molecule, will give you unique electrical signals. However, to be completely biocompatable, the nanowire would have to be non-toxic.

It's like a DNA test for molecules: Physical properties affect the molecular signatures of the chemicals. Before taking chemical sensors around town, the researchers tired to figure out which molecules give off certain signals, so they used computation models to help them nail down a number of chemical fingerprints.

"These platforms can generate an electric signal and act as their own power source," Wang said. By converting chemical energy into electricity, the fact that the sensor can engage in energy harvesting makes it...well, that much more interesting. It can power other nanodevices, or be used any other time when you need a battery.

Before this chemical detector can be of any real use, the researchers will have to figure out how to make it sniff out more complex chemicals commonly found in explosives or in the human body. So far, the researchers have shown that the main use will be... detecting home-made bombs.

I think Wang has a good chance at getting his sensors out of the lab and into the real world. However, Wang's battery-less sensor isn't the only new kind in town. For instance, some sensors can get their charge by hooking up wirelessly.

via Lawrence Livermore National Laboratory

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