Hygiene: "The sensor applies the principle of so-called photonic structures"

Interview with Prof. Holger Schönherr, Department of Physical Chemistry, University of Siegen

Detecting infections quickly and reliably with the naked eye: This is what many doctors in hospitals and in the doctor's surgeries wish for. To make this dream come true, Prof. Holger Schönherr, a scientist from Siegen, is researching a sensor that should show an infection by a color change.


Photo: Researcher with glasses at a microscope - Prof. Holger Schönherr; Copyright: University of Siegen

Prof. Holger Schönherr; ©University of Siegen

Prof. Schönherr, how does the sensor that your team developed work?

Prof. Holger Schönherr
: The sensor applies the principle of so-called "photonic structures". You can find those structures on the wings of butterflies for instance. This is coloring that makes due without dyes. The foundation is a special structure, which we can replicate with silicon or aluminum oxide. You can imagine it like this: the material has pores and depending on what is in the pores, assuming air and liquid, the color changes with a modification. This also works if you degrade or attach a layer on the pore wall. In other words, changes are happening inside the pores, which lead to a color change - the principle is ultimately an overlapping of light waves. In nature for instance, this happens in butterflies, which appear to have a different color depending on the exposure to light.

You want to develop an adhesive bandage that changes color if infection spreads in burns. What exactly would happen inside the material?

: You would design the pores to where they react to specific attachment and degradation processes of bacterial secretion. I could also imagine that the entire pore is filled with an enzyme sensitive material, which is then broken down. This would open up the pore and change the refractive index, which in turn leads to a color change.
Photo: Photonic crystal that glows green and red; Copyright: H. Schönherr et al.

Green turns to red: with a color change, a nanoporous silicon photonic sensor indicates air exchange in the nanopores with alcohol. In the future, infections are meant to be indicated based on the same principle; ©H. Schönherr et al.

Would there be several areas of application possible for such an adhesive bandage or would it be restricted to a specific application?

: This depends on what material is being used. In another project, we investigated and developed approaches to selectively show enzymes of bacteria or toxins that are produced by pathogenic bacteria. Of course, enzymes are very specific to a certain degree. However, pathogenic bacteria - pseudomonas, staphylococci - have their own enzyme spectrum. Nevertheless, there are also enzymes that are produced by different bacteria. This is why the fundamental question is whether I develop a sensor that generally responds to different bacteria or one that is specifically geared towards one bacterium. In the case of burns for example, there are different types of bacteria. When you concentrate on all of them, there is certain likelihood that you detected the infection.

There are already different approaches to develop a so-called "intelligent adhesive patch" where a color change also takes place. Different pH values were being measured in this case. What is the advantage of your method?

: It starts at a more important spot. A change in pH value is generally very non-specific and a wound that heals runs through entire pH value ranges. At the end of the day, we detect bacteria directly through enzymes, which is ultimately much more reliable.

You also collaborate with scientists from Australia for this project. Do you consider it an advantage to work with a global network on such a project?

: Yes, because you can utilize the expertise of the other party. As part of a larger Australian program, the Mawson Institute at the University of South Australia in Adelaide has other options available than we have here. This pertains to the infrastructure and existing local networks. Besides, you cannot find solutions for complex problems on your own. The fact that it is Australia and not another city in Germany is due to the nature of the current projects. The Australians have started a big program that is focused on chronic wounds. In Europe on the other hand, there was a big program on the subject of "burns". We found a common denominator and found out that we make a great team together. There is a mutual synergy. This is a very positive aspect and essential for both the project and the doctoral candidates.
Photo: Simone Ernst; Copyright: B. Frommann

© B. Frommann

The interview was conducted by Simone Ernst and translated from German by Elena O'Meara.