A fabrication method was developed to create dyed threads that change color when they detect a variety of gases. 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, the gas-detecting threads could provide a reusable, washable, and affordable safety asset in medical, workplace, military, and rescue environments.
While not replacing the precision of electronic devices commonly used to detect volatile gases, incorporating gas detection into textiles enables an equipment-free readout without the need for specialized training. Such an approach could make the technology accessible to a general workforce or to low-resource communities that can benefit from the information the textiles provide.
A manganese-based dye (MnTPP), methyl red, and bromothymol blue were used 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. A three-step process “traps” the dye in the thread. The thread is first dipped in the dye, then treated with acetic acid, which makes the surface coarser and swells the fiber, possibly allowing more binding interactions between the dye and tread. Finally, the thread is treated with polydimethylsiloxane (PDMS) that creates a flexible, physical seal around the thread and dye and 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 dyes work in different ways to detect gases with different chemistries.
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 and quantify the color changes or interpret color signatures using multiple threads and dyes. Detection could be scaled up to measure many analytes at once or to distinguish analytes with unique colorimetric signatures.
The fabric even works underwater, detecting the existence of dissolved ammonia. While the PDMS sealant is hydrophobic and keeps water off the thread, the dissolved gases can still reach the dye to be quantified. Since repeated washing or use underwater does not dilute the dye, the fabric can be relied upon for consistent, quantifiable detection many times over.