Signaling Skin pH with Indicator Dyes

By: Katie Schaefer, Cosmetics & Toiletries magazine

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

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Mohr and his team therefore designed dyes to be more precise than a pH electrode by mixing them.

“By combining [dyes], we cover the whole pH range with high sensitivity,” he said.

Although Mohr could not indicate which dyes his team uses, he noted they have a similar structure to food dyes and are currently being investigated for safety. After developing the dyes, the team considered other applications for the technology, at which point they began investigating wound dressings.

Indicating Infection

In addition to sensitivity across a broad pH range, for wound dressings, the dyes also needed to exhibit perceptible color changes and remain stable when immobilized in polymer material. “The chromophore, or color-carrying structure, must absorb in the visible spectral range,” Mohr explained.

Also, similar to their use in water treatment, the dyes needed to change color at a specific pH range. According to the researchers, a pH of 6.5–8.5 indicates infection; if the skin beneath the dressing is healthy, its pH typically is below 5.