Scientists invent threads to detect gases when woven into clothing

Engineers from Tufts University, USA have developed a novel fabrication method to create dyed threads that change color when they detect a variety of gases. The researchers demonstrated that the threads can be read visually, or even more precisely by use of a smartphone camera, to detect changes of color due to analytes as low as 50 parts per million. Woven into clothing, smart, gas-detecting threads could provide a reusable, washable, and affordable safety asset in a medical, workplace, military, and rescue environments.

The study used a manganese-based dye, MnTPP, methyl red, and bromothymol blue to prove the concept. MnTPP and bromothymol blue can detect ammonia while methyl red can detect hydrogen chloride - gases commonly released from cleaning supplies, fertilizer and chemical and materials production. The thread is first dipped in the dye, then treated with acetic acid, which makes the surface coarser and swells the fiber. Finally, the thread is treated with polydimethylsiloxane (PDMS), which creates a flexible, physical seal around the thread and dye, which also repels water and prevents dye from leaching during washing. Importantly, the PDMS is also gas permeable, allowing the analytes to reach the optical dyes.

The team used simple dyes that detect gases with acid or base properties. The tested dyes changed color in a way that is dependent and proportional to the concentration of the gas as measured using spectroscopic methods. In between the precision of a spectrometer and the human eye is the possibility of using smartphones to read out and quantify the color changes or interpret color signatures using multiple threads and dyes. 

The threads even worked under water, detecting the existence of dissolved ammonia. Since repeated washing or use underwater does not dilute the dye, the threads can be relied upon for consistent quantifiable detection many times over, the researchers said.