Fluorescent Bandage Monitors Healing Process

A smart wound dressing with integrated pH sensors provides continuous information on the state of the healing process within chronic wounds.

Under development by the Swiss Federal Laboratories for Materials Science and Technology (Empa; Dübendorf, Switzerland), Centre Suisse d’Electronique et de Microtechnique (CSEM; Neuchâtel, Switzerland), and other institutions, the bandage is based on a novel hydrophobic ion pair of pyranine and benzalkonium. The pyranine component is a non-toxic fluorescent dye--also found in highlighters--that allows precise ratiometric detection of pH under ultraviolet (UV) light, especially at pH levels between 5.5 and 7.5.


Benzalkonium, a quaternary ammonium salt with potent antimicrobial properties, makes the pyranine element sufficiently hydrophobic to allow its incorporation in conventional membranes and commercial wound dressings while maintaining its pH sensing performance unaffected. It also confers the resulting ion pair strong antimicrobial properties. If a wound heals normally, the pH rises to 8 before falling to 5-6; but if the wound fails to close and becomes chronic, pH level fluctuates between 7 and 8.

The bandage can therefore inform nursing staff if wound pH is permanently high. On the other hand, if the bandage does not need changing for reasons of hygiene and pH levels are low, they could afford to wait. The researchers are now in the process of developing a portable device capable of monitoring several fluorescence parameters at once, such as glucose and oxygen levels, while the wound heals. If parameters change, conclusions key biochemical processes involved in wound healing can be drawn. A study describing the bandage was published in the October 2017 issue of Sensors and Actuators.

“The idea of a smart wound dressing with integrated sensors is to provide continuous information on the state of the healing process without the bandages having to be changed any more frequently than necessary. This would mean a gentler treatment for patients, less work for the nursing staff, and therefore lower costs,” said senior author Luciano Boesel, PhD, of the Empa Laboratory for Biomimetic Membranes and Textiles. “You don’t have to cover the entire surface of wound dressings with sensors. It’s enough for a few small areas to be impregnated with the pyranine benzalkonium molecules and integrated into the base material.”

pH (potential of hydrogen) is a numeric scale representing the negative of the logarithm to base 10 of the activity of the hydrogen ion. Solutions with a pH less than 7 are acidic and solutions with a pH greater than 7 are basic. Pure water is neutral, at pH 7, being neither an acid nor a base.

Related Links:
Swiss Federal Laboratories for Materials Science and Technology
Centre Suisse d’Electronique et de Microtechnique