As Swiss forests increasingly embrace the planting of deciduous trees, which often face direct incineration, the need for innovative solutions to sustainably utilize Swiss hardwood is more pressing than ever.
Researchers at Empa are, therefore, enhancing wood with novel functionalities. Their latest achievement: wood that emits light in the dark.
To combat climate change and the threat of bark beetle, additional deciduous trees are being cultivated in Swiss forests. Ideally, their wood should undergo multiple uses before being transformed into firewood, thereby releasing the carbon dioxide it had previously sequestered back into the atmosphere.
Currently, hardwood is still too often utilized immediately for heating purposes. Consequently, there is a need for innovative concepts that promote more sustainable cascading use. One option is to impart new properties to the natural material—in technical jargon, these are referred to as functionalities—allowing it to be transformed into variants that are magnetic, waterproof, or capable of generating electricity, for example.
A team led by fungal specialist Francis Schwarze from Empa’s Cellulose & Wood Materials laboratory in St. Gallen is currently exploring another concept for producing a new type of composite material derived from hardwood: luminous wood. Beyond its potential technical applications, this luminous wood could also be crafted into designer furniture and jewelry.
This accomplishment is possible due to a parasite: the honey fungus acts as a pathogen responsible for white rot in trees, making it a wood pest. Certain species generate the natural compound luciferin, which is activated to emit light through a two-step enzymatic process. Consequently, wood invaded by fungal filaments radiates a green luminescence.
“Naturally luminous wood was first described around 2,400 years ago by the Greek philosopher Aristotle,” says Schwarze. Strictly speaking, the interwoven structure of fungus and wood can be described as a natural biohybrid, a combination of living materials. “Artificially produced composite materials of this kind would be interesting for many types of application,” says the Empa researcher.
What nature accomplishes with ease has long posed significant challenges for biotechnology. However, the Empa team has made a groundbreaking advancement by successfully inducing and controlling this process in the lab for the first time.
Biotechnologist Francis Schwarze has discovered glowing mushrooms in the wild, meticulously analyzed them in the laboratory, and cracked their genetic code. Among these, the ringless honey fungus (Desarmillaria tabescens) has proven to be exceptionally potent.
After conducting preliminary tests with various wood types, Schwarze focused on balsa wood (Ochroma pyramidale), renowned for its low density. Through spectroscopy, the researchers meticulously observed how the fungus breaks down lignin in the balsa wood samples, which contributes to the wood’s stiffness and compressive strength.
However, X-ray diffraction analyses revealed that the wood’s stability remains unaffected: the cellulose, which is responsible for the wood’s tensile strength, stayed intact.
Experience the captivating brilliance of the biohybrid created from fungus and wood as it reaches its peak luminosity after three months of incubation. Desarmillaria flourishes in moisture-rich environments, allowing balsa wood samples to absorb an astonishing eight times their weight in water during this period.
The enzyme reaction within the wood is activated upon exposure to air. After approximately ten hours, the glow reveals its full brilliance, producing a green light with a wavelength of 560 nanometers, as identified by Empa researcher Giorgia Giovannini from the Biomimetic Membranes and Textiles lab through fluorescence spectroscopy studies. At present, this captivating process continues for around ten days.
“We are now optimizing the laboratory parameters in order to further increase the luminosity in the future,” says the Empa researcher.
