Engineers from Tufts University want to make the detection of pollutants or dangerous chemicals as simple as checking the color of your T-shirt.

The university's novel fabrication method creates dyed threads that change color when sensing volatile organic compounds such as acidic vapors and ammonia. The researchers demonstrated that the threads can be read visually, or even more precisely with a smartphone camera, detecting analytes as low as 50 parts per million.

Woven into clothing, the Tufts team sees the gas-detecting threads as a reusable, washable safety asset in medical, military, and rescue environments. The equipment-free approach additionally makes the textiles an intriguing option for the general workforce or low-resource communities.

The study, published in the journal Scientific Reports, describes the fabrication method and its ability to extend to a wide range of dyes and detection of complex gas mixtures.

The team used simple dyes to detect gases with acid or base properties. The demonstration's three indicators included: a manganese chloride known as MnTPP; methyl red (MR); and bromothymol blue (BTB). MnTPP and bromothymol blue can detect ammonia while methyl red indicates the presence of hydrogen chloride — gases commonly released from cleaning supplies, fertilizer, and chemical and materials production.

Sensing threads from Tufts university that detect gases and pollutants including acid and ammonia
Sensing threads prepared with bromothymol blue (top thread), methyl red (middle thread) and MnTPP (bottom thread) are exposed to ammonia at 0 ppm (left panel) 50 ppm (middle panel) and 1000 ppm (right panel). (Image Credit: Rachel Owyeung, Tufts University, Nano Lab)

The fabrication process has three parts.

The thread is first dipped in the dye, then treated with acetic acid, which swells and coarsens the fiber, increasing binding interactions between the dye and thread. Finally, the thread is treated with polydimethylsiloxane (PDMS), which creates a flexible, water-repelling seal. Importantly, the PDMS is also gas permeable, allowing the analytes to reach the optical dyes.

"Since we are using a method that effectively traps the dye to the thread, rather than relying so much on binding chemistry, we have more flexibility to use dyes with a wide range of functional chemistries to detect different types of gases," said Sameer Sonkusale, professor of electrical and computer engineering at Tufts University's School of Engineering who heads the Nano Lab at Tufts and is corresponding author of the study.

The tested dyes changed color in a way dependent and proportional to the concentration of the gas as measured using spectroscopic methods.

Smartphones can also be used to read out, quantify, and interpret color signatures using multiple threads and dyes.

"That would allow us to scale up the detection to measure many analytes at once, or to distinguish analytes with unique colorimetric signatures," said Sonkusale.

Sonkusale and Rachel Owyeung, lead author and graduate student in the Tufts Department of Chemical and Biological Engineering, spoke with Tech Briefs about where these kinds of smartly sewn fabrics could be most valuable.

Tech Briefs: What inspired this idea?

Rachel Owyeung: Current methods to monitor pollution or harmful gases require dedicated sensors and equipment. We wanted to explore a solution that can be integrated into something you would already have on you, such as, in our case, the clothes you wear, like your T-shirt. The platform lets you be cognizant of a hazardous environment before you've exposed yourself to dangerous levels, which is a powerful tool when monitoring environments.

Tech Briefs: How is the gas able to affect the colors of the thread?

Rachel Owyeung: The threads change color because the color changing chemical dyes that are entrapped on the fibers of the thread, which undergo a chemical conformation change as a result of a compound being present in the gas.

Tech Briefs: What kinds of gases can be detected? What gases did you detect in early tests?

Rachel Owyeung: There are thousands of color dyes that are responsive to many gases and chemicals. What you can therefore detect depends on the choice of optical dyes. By adding multiple dyes that respond to different target gases, we can improve the sensitivity and selectivity of our sensing platform.

So, in theory we can monitor many volatile gases commonly found today in the environment such as those produced by petrochemicals, oil and gas heating, cleaning supplies, automobile and industrial exhausts, underground mines, etc. For proof of concept, we showed gas detection of a few common volatile organic compounds such acidic vapors and ammonia, and can readily work for detection of petroleum distillates such as ethanol.

Tech Briefs: What role does the smartphone play in the detection?

Rachel Owyeung: The smartphone captures the images of the sensors before and after exposure to a particular gas. One could imagine a smartphone app in which a baseline photo for the threads is already established. The user could then upload a photo of the threads and the app would return the type and amount of a gas present, due to the differences in color between the two images.

an illustration of thread-based sensors from Tufts University
Concept of the gas sensing washable threads. Illustrates the thread-based sensors integrated into a textile patch. As the gas passes over the patch, the optical dye changes conformation, resulting in a color change. Color change is determined via smartphone readout. (Image Credit: Tufts University, Scientific Reports)

Tech Briefs: How do you envision the sensors being used?

Rachel Owyeung: Since our sensors are thread-based and can be fabricated easily, we envision these could be incorporated into existing clothing and personal protective equipment, such as a lab coat, where one might be in the presence of something hazardous. One can imagine a lab worker walking into a room where there has been a small chemical spill, and their lab coat changes color due to the hazardous gases present. Or you can imagine your shirt changing color as you enter an old apartment building because the heating system is leaking exhaust fumes into the house ventilation system.

Tech Briefs: What is most exciting to you about this process and its possibilities?

Sameer Sonkusale: We initially intended for these sensors to be used in textiles, so we created a robust coating method that would allow them to be washable, yet still retain their sensing abilities. We like the fact that this will empower each and everyone to monitor the environment they live and work in. Beyond monitoring volatile gases in the environment, We recently realized that our sensors could be used for monitoring gases dissolved in water, which is otherwise nontrivial because the water would typically wash away the dyes. We can possibly monitor water quality. Expanding this application to look for dissolved gases in biological fluids could make these threads a powerful medical diagnostic tool as well.

What do you think? Where do you see these smart threads being used? Share your comments and questions below.