Researchers from Trinity College Dublin and the SFI Research Centre for Advanced Materials and BioEngineering Research (AMBER) have developed a novel set of microscopic gas sensors using 3D printing technology.
Designed to mimic the color-changing feathers of a peacock, the 3D printed sensors are capable of changing colors in the presence of certain solvent vapors. As such, they can be used to provide a very visual manner of detecting hazardous pollutants, all while being cost-effective to manufacture.
The team believes its devices could have major implications for real-time gas monitoring in homes, cars, and workplaces, as well as in wearable devices for personal health applications.
Professor Larisa Florea, a co-author of the study, explains, “We have created responsive, printed, microscopic optical structures which can be monitored in real-time, and used for the detection of gases. The ability to print such an optically responsive material has profound potential for their incorporation into connected, low-cost sensing devices.”
Why do we need to monitor gases?
It’s not a stretch to say that the average person spends the majority of their time indoors these days, whether that be at home, in a vehicle, or in an office. According to Florea, the concentration of pollutants found indoors can be anywhere from 5 – 100 times greater than the concentration found outdoors. The unnerving nature of the figure is amplified when you consider that the World Health Organization suggests 90% of the world’s population lives in areas that exceed acceptable air standard limits.
As it stands, modern-day indoor gas sensors focus almost exclusively on leaks, smoke, or carbon monoxide detection, leaving niches such as real-time volatile organic compound (VOC) and ammonia detection largely unaddressed.
Placing a greater focus on a comprehensive (but low-cost) environmental monitoring ecosystem can ultimately help make human health a more crucial consideration in home building and manufacturing facilities.
3D printing the color-changing gas sensors
Developing the gas sensors, the team had to design, model, and prototype a set of microscopic structures using their own in-house stimuli-responsive 3D printing materials. To enable such tiny structures, the researchers leveraged the process of two-photon polymerization, a very precise form of SLA-based 3D printing where a spot laser is used to cure resins into microscopic parts.
These printed sensor structures, interestingly, drew inspiration from the feathers of a peacock, which are known to change colors depending on the angle they’re viewed at. This property is called iridescence.
Dr Colm Delaney, lead author of the study, explains, “More than 300 years ago, Robert Hooke first investigated the vibrant colours on a peacock’s wing. Only centuries later did scientists discover that the effervescent colouration 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.”
Delaney’s team eventually managed to get the 3D printed sensors to change colors in response to different solvent vapors. This was done by varying the formulation of the material used as well as the geometry of the structures, since the viewing angle was also a factor in how the sensors reflected light. Despite being smaller than a freckle, they proved useful for revealing the contents and chemistry of the environment they were in. As a bonus, the 3D printed sensors are low-cost, adaptable to different stimuli, require minimal power consumption, and are highly sensitive.
Further details of the study can be found in the paper titled ‘Direct laser writing of vapour-responsive photonic arrays’.
Additive manufacturing’s extensive material compatibility lends itself quite well to sensor device applications. Earlier this year, engineers at Washington State University (WSU) and DL ADV-Tech used 3D printing to develop a means of detecting exposure to the potentially-carcinogenic herbicide glyphosate. Composed of a series of nanotubes coated with 3D printed sensors, the test kit uses similar tech to that found in diabetic glucose monitors, only it deploys currents to assess glyphosate levels instead.
Elsewhere, researchers at Santa Clara University recently used 3D printing to build an upgraded version of the hydration sensing units deployed in agricultural irrigation systems. By redesigning, 3D printing and iterating on parts of these sensors, the engineers have been able to improve their thermal detection capabilities, and shrink their overall size.
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Featured image shows SEM imaging of the microscopic gas sensors. Image via Trinity College Dublin.