How Chemical Sensing Devices Work

smoke and carbon monoxide detector smoke and carbon monoxide detector
A Nest smoke and carbon monoxide detector is seen on Jan. 16, 2014, in Provo, Utah. George Frey/Getty Images

Breathing in and out is something our bodies do without our having to think about it. In fact, we rarely even give a second thought to the air surrounding us until the quality is low somehow – maybe from the smoke of a nearby fire or smog enveloping our crowded cities.

But there can be dangerous gases that are not always visible. Carbon monoxide and radon are two examples of deadly air contaminants that are completely invisible. We don't realize we're being poisoned from the air we breathe until it is too late. Luckily, these gases aren't that prevalent, and with the help of a little chemical sensing technology, we can let carbon monoxide and radon detectors do the worrying for us.

Chemical sensors are helpful far beyond just detecting deadly gases. These devices can be found in our homes, hospitals and in the military. There are many different types of sensors that detect different target molecules (also known as analytes). Although the sensors work in various ways, the gist is that a chemical interaction happens between the analyte and something in the sensor, and the device produces a measurable signal – a beeping or a color change to alert us to the presence of the target molecule.

Despite the differences in the construction of sensors, there are a few guiding principles that make any sensor good. The ideal one is inexpensive, foolproof and portable. Most importantly, any chemical sensor has two vital features: selectivity and sensitivity. There are more than 10 billion molecular substances in the world, so selectively detecting a single substance is no small feat [source: National Research Council]. Sensitivity is also incredibly important for detecting chemicals from a considerable distance or for trying to find very low concentrations of a target molecule. Other important sensor features are response time, packaging size and limit of detection — the lowest quantity of a substance that can be detected.