A team of scientists have discovered a way to create ultra-compact gas sensors which change color to alert of a range of solvents — using a high-resolution form of 3D printing.
"We have created responsive, printed, microscopic optical structures which can be monitored in real-time, and used for the detection of gases," Larisa Florea, professor at Trinity College Dublin, explains. "The ability to print such an optically responsive material has profound potential for their incorporation into connected, low-cost sensing devices for homes, or into wearable devices for monitoring analytes."
Dubbed "photonic sensors," the tiny color-changing gadgets are created using direct laser writing (DLW) — a form of 3D printing aimed at a microscopic scale, capable of producing a feature resolution of just 200nm. "The resulting periodic structures," the team explains, "swell reversibly in the presence of solvent vapors, to generate a measurable optical response which is determined by the polarity of the solvent."
The concept itself is inspired by nature. "More than 300 years ago, Robert Hooke first investigated the vibrant colors on a peacock's wing. Only centuries later did scientists discover that the effervescent coloration was caused not by traditional pigments but by the interaction of light with tiny objects on the feather, objects which were just a few millionths of a metre in size," Colm Delaney, PhD and lead author, explains.
"We have taken this biological design, seen all the way from a magpie to a chameleon, to make some really exciting materials. We achieve this by using a technique known as Direct laser-writing (DLW), which allows us to focus a laser into an extremely small spot, and to then use it to make tiny structures in three dimensions from the soft polymers which we develop in the lab."
“To date, indoor gas sensors have focused almost solely on leak, smoke, and carbon dioxide detection," says Florea. "Even iterative advances, to include relative humidity, oxygen levels, carbon dioxide, volatile organic carbons (VOCs), and ammonia in a real-time manner could play an enormous role in the development of a domestic environmental monitoring ecosystem. This could ensure that health and well-being monitoring become central to the future of home building and automation.”
The team believes that the same approach can be used beyond gas sensors, too, suggesting that the same form of sensor could detect changes in the local chemical environment, temperature, light, or even electric fields.
The team's work has been published in the Journal of Materials Chemistry C and is available under open-access terms as a downloadable PDF.