Signaling Skin pH with Indicator Dyes

By: Katie Schaefer, Cosmetics & Toiletries magazine

Posted: January 3, 2011, from the January 2011 issue of Cosmetics & Toiletries.

In wound care, dressings protect the skin while it heals. To effectively protect against infection, however, the dressing must be strongly affixed to the skin, which can result in an injurious and painful removal for the patient. This experience, generalized by the expression “ripping off the bandage,” could become a thing of the past, though, as Gerhard Mohr, PhD, head of the sensor materials group at The Fraunhofer Research Institution for Modular Solid State Technologies (EMFT), has developed dyes for wound dressings that change color when they detect infection. Interestingly, initial research for this wound-healing application originated in the water treatment field.

Beginnings in pH Detection

According to Mohr, research to develop his indicator dyes began in aquaculture.

“[My team] had a project to simultaneously detect ammonia and pH in water,” he said, explaining their device continuously tested water for ammonia and pH. “Fish in these environments make their water basic [when they expel ammonia], so the pH changes from neutral to alkaline, which is not good for the fish; if the pH gets too high [i.e. basic], the fish die.”

For this device, Mohr’s team used indicator dyes that change color with the change in pH. Like litmus paper, the dyes showed a marked change; however, it was important to create indicator dyes that were sensitive across a range of pH values.

“The problem with indicator dyes is that they are highly sensitive [within] a limited region, pH 6– pH 9. You can measure precisely in this range but not outside of it.”