Researchers at Tufts University in the US developed a new fabrication method to create dyed threads that change colour when exposed to harmful gases like ammonia and hydrogen chloride.

As a proof of concept, the researchers used a manganese-based dye called MnTTP, methyl red and bromothymol blue as dyes. MnTTP and bromothymol blue can detect ammonia, while methyl red detects hydrogen chloride, gases commonly released from cleaning supplies and fertilisers. The threads are dipped in the dye, treated with acetic acid (which makes the surface coarser and swells the fibre), and finally treated with polydimethylsiloxane (PDMS), which creates a flexible physical seal around the thread and dye and also repels water. PDMS also prevents the dye from leaching during washing and is gas permeable. Thanks to this method, the researchers have a flexibility to use dyes with a wide range of functional chemistries to detect different types of gases.

The tested dyes change colour in a way that can be read visually, or be more precisely measured with a. smartphone camera. The dyes even work underwater, detecting the existence of dissolved ammonia. As the dye is not diluted by washing or being in water, the thread can be used many times over.

Woven into clothing, the colour changing threads provides a reusable, washable, and affordable safety asset for, for instance, medical or military personnel.

Photo: Tufts University