Colorimetric detection of ammonia using an adhesive, stretchable hydrogel patch

Currently, because of the harmful effects of ammonia on human health, ecosystems, and overall air quality, the development of easily usable, portable, cost-effective, and field-deployable ammonia sensors is urgently necessary. This study focused on the development of an ammonia-sensing patch composed of a fibrous sensing component and hydrogel-like support substrate. This sensor was capable of colorimetric ammonia sensing with a limit of detection of 0.2454 ppm. The fibrous sensing region was prepared by electrospinning a mixture of poly(acrylic acid) (PAA) and poly(vinyl alcohol) (PVA), followed by the partial crosslinking and adsorption of transition metal ions such as copper. A support substrate was prepared by combining PVA and borate compounds, resulting in a stretchable, adhesive, and self-healing hydrogel. The ammonia-sensing patch demonstrated enough adhesion to various substrates and could be used as a sticky plaster-type sensor that also function as a sealant. The patch exhibited a distinct color change from blue–green to blue upon exposure to ammonia gas, which was attributed to the formation of a complex between the copper ions and ammonia. The color change was analyzed by monitoring the average RGB intensities using a charge-coupled device (CCD) camera and a MATLAB program. Additionally, we assessed the patch's capability of detecting and sealing ammonia leakage through experiments conducted in a simulated gas leakage setup. Overall, the developed ammonia-sensing patch shows promise for the real-time colorimetric detection of ammonia gas and has potential applications in gas leakage detection and prevention.