Chemical engineers at the University of Wisconsin-Madison have combined computational chemistry and liquid crystals to develop a way to create potentially inexpensive, portable sensors to detect everything from explosives to disease markers in a person’s breath.

Manos Mavrikakis and Nicholas Abbott.Manos Mavrikakis and Nicholas Abbott, professors of chemical and biological engineering, developed a framework for optimizing the components of a liquid-crystal-based sensor: metal cations, or positively charged ions; salt anions, solvents and molecules that form liquid crystals.

The research involved cycling between quantum chemical modeling and laboratory experiments to optimize the sensor components for a targeted substance. By tweaking each of the individual components in turn, they identified an ideal configuration that specifically responded to the molecule they wanted to sense, called the analyte.

The same approach, they say, could yield new sensors for a host of different analytes to indicate, for example, the freshness of fish or meat based on the presence of trace amounts of the molecule cadaverine. Another variation might be used to detect respiratory diseases based on analysis of small molecules such as nitric oxide in breath.

Their sensor material consists of a thin film of metal salt, with liquid crystals anchored to the surface all pointing in the same direction. The researchers designed specific liquid crystal molecules and metal cations so that small amounts of analyte would disrupt the interactions of the liquid crystals with the surface, and throw the ordered arrangement into disarray. The change in the liquid crystal would be a visible indicator of the analyte’s presence.

Unlike expensive explosive-detecting puffer machines in airports that rely on complicated mass spectrometry or high-performance liquid chromatography equipment, these liquid crystal sensors could be portable, wearable and inexpensive, the researchers said.

They plan to investigate new combinations for additional analytes and develop new liquid crystalline molecules, in combination with other metal salts and solvents, to make even more sensitive and selective sensors.