Shining a light on germs

Antibiotic-resistant bacteria and emerging viruses are a rapidly increasing threat to the global healthcare system. Around 5 million deaths each year are linked to antibiotic-resistant germs, and more than 20 million people died during the COVID-19 virus pandemic. Empa researchers are therefore working on new, urgently needed strategies to combat such pathogens. One of the goals is to prevent the spread of resistant pathogens and novel viruses with smart materials and technologies.

Surfaces that come into constant contact with infectious agents, such as door handles in hospitals or equipment and infrastructure in operating theaters, are a particularly suitable area of application for such materials. An interdisciplinary team from three Empa laboratories, together with the Czech Palacký University in Olomouc, has now developed an environmentally friendly and biocompatible metal-free surface coating that reliably kills germs. The highlight: The effect can be reactivated again and again by exposing it to light.

Biocompatible: Stable and safely embedded in a compatible polymer, graphenic acid is deadly for germs. Image: Empa

“The new material is designed to kill microorganisms locally and quickly,” explains Giacomo Reina from Empa's Nanomaterials in Health Laboratory in St. Gallen. A basic matrix of polyvinyl alcohol, a biocompatible plastic that is also used in the food industry, was used for this purpose. Embedded in this matrix is specially synthesized graphenic acid, which is ideally suited as an antimicrobial coating due to its chemical properties. Its full potential can be exploited by using near-infrared light. As soon as the composite material is irradiated, it unfolds its dual strategy: Firstly, it absorbs the energy of the infrared light and converts it into germicidal heat. It also stimulates the formation of oxygen radicals, which cause additional damage to the pathogens.

Another advantage here is that this strategy is completely different from the mode of action of conventional antibiotics. The material thus offers continuous protection against a broad spectrum of microorganisms without contributing to the development of resistance. “Our laboratory experiments have clearly confirmed the effectiveness of the antimicrobial material against various bacteria and viruses,” says the Empa researcher.

Antibiotic resistance: One of the most dreaded germs in the oral cavity is the bacterium Pophyromonas gingivalis, a pathogen that causes severe periodontitis with increasing antibiotic resistance. Image: Adobe Stock.

An initial application for the antimicrobial coating is currently being developed for dentistry. To this end, Empa researchers are working together with the Center for Dental Medicine at the University of Zurich on a dental splint that kills microorganisms in the oral cavity.

The microbial flora in the mouth is a particularly unpleasant opponent in the fight against infectious agents: Complex communities of bacteria cavort in inaccessible niches, embedded in a self-produced mucous matrix. Antibiotics and disinfectants barely penetrate these resistant biofilms. This allows the germs to ruin teeth unhindered or even lead to extensive infections in the body. The interdisciplinary team led by Giacomo Reina is therefore working on a plastic splint into which nanomaterials such as graphenic acid can be stably integrated. As near-infrared light can penetrate the tissue several centimeters deep, the splint can be placed in the oral cavity and activated from the outside by a light source, over and over again.

The project can be started thanks to generous donations from the Eduard Aeberhardt Foundation and another foundation. Clinic Director Ronald Jung from the Center for Dental Medicine at the University of Zurich appreciates this interdisciplinary approach to materials science and clinical research. “Such new and innovative solutions will offer great added value for patients,” says Jung.