A Novel Approach to Chemical Sensor Design

Chemical sensors, oxygen tanks and other equipment inside a case during a joint chemical warfare training session by U.S. soldiers and marines at Camp Buehring, Kuwait.)

A team of chemical engineers recently developed a new approach to designing the chemical sensors used to detect explosives, pollutants and even disease. The team’s approach allows them to tune sensor components for different chemicals, resulting in effective yet inexpensive sensors.

Optimizing Liquid Crystal Sensors

The engineers’ approach uses liquid-crystal-based chemical sensors, which are based on technology similar to that found in LCD TVs. They consist of metal cations, salt anions, solvents and molecules that form liquid crystals.

The sensors work using nematic liquid crystals anchored to a thin film of metal salt, all with the same orientation. If the liquid crystals and metal cations are designed in the right way, small amounts of the target chemical (called the analyte) will disrupt the interactions between the liquid crystals and the film surface, throwing off the ordered arrangement.

Shown are the minimum energy structures of metal cations bound to (a) benzonitrile (PhCN) and (b) dimethyl methylphosphonate (DMMP). (Image and caption courtesy of Nature Communications.)

But while the general principle is fairly straightforward, the difficulty lies in properly designing the liquid crystal molecules and metal cations. To target a specific chemical substance, the components of the liquid crystal sensor must be specifically optimized.

Solving this problem is where the researchers took a new, first-principles approach. Instead of a laborious process of trial and error, the engineers made use of quantum chemical modelling and computer simulations before turning to laboratory experiments.

“This is indeed the first time that computational chemistry with quantum mechanics has been used to put together a coherent way of thinking for narrowing down possible solutions for an explosively complicated problem,” said researcher Manos Mavrikakis.

Low-Cost Chemical Sensors

This same approach could speed up development of chemical sensors for a number of different analytes. For example, sensors could be designed to indicate the freshness of meat and fish by detecting the molecule cadaverine. Or, by analyzing breath for molecules like nitric oxide, sensors could be used to detect certain respiratory diseases.

Another benefit of the liquid crystal sensors is that they’re less expensive than alternative sensors, such as those that rely on mass spectrometry or high-performance liquid chromatography. Since they’re also more portable, the liquid crystal sensors may be a good candidate for wearable technology.

The engineers are planning to continue their research, by exploring new liquid crystal molecules and analyte combinations to make more sensitive and selective sensors. You can read their paper in Nature Communications.

For more sensor news, check out Beyond the Apple Watch: How Quantum Sensors will Change the World.