For many years, diagnostic labs have used colour change as a marker for the growth of specific microbes. Think of all those chromogeneic agar plates that your lab goes through each day. And there are all sorts of broths that change colour in response to specific chemical changes caused by microbial growth. One of the first projects I was ever involved with was environmental sampling for MRSA at Lewisham hospital, where we used a selective broth that turned bright yellow when MRSA was present. So in a way, it is surprising that this approach has not been adopted as a marker to indicate wound infection.
Scientists at Bath Uni have developed a neat novel wound dressing that fluoresces when the early signs of an infection are present. The concept is simple: a gel containing tiny sacs of dye are included in a hydrogel dressing; if cytotoxins that are indicative of bacterial infection are present, they lyse the sacs and release the dye, which fluoresces under UV light.