Chromogenic ecdysis of Au@Ag nanorods assembled in a hydrogel for selective detection of ammonia vapors in food.

Chromogenic sensors are highly appreciated, but the color change must be significant to clearly indicate the change. We proposed a hydrogel sensor containing Au-bead@Ag nanorods for the detection of ammonia to ascertain the shelflife of meat. Polymers with different water-holding capacity were tested. Agarose gel had the required amount of water to capture ammonia to show a significant visible color change as a function of different ammonia concentrations. Microscopy and X-ray photoemission spectroscopy (XPS) showed the captured ammonia tuned the pH to dissolve Ag in Au-bead@Ag nanorods into ions/clusters/alloys for the color change. The color changed from orange to blue-green in the gel after 3 h of exposure to an ammonia-spiked meat sample.