ST. GALLEN, Switzerland — A team led by fungal researcher Francis Schwarze from Empa's Cellulose & Wood Materials lab in St. Gallen is currently pursuing another idea for a new type of composite material based on hardwood: luminous wood. In addition to applications in technical fields, the luminous wood could be processed into designer furniture or jewelry.

The idea behind their research is that hardwood should be used several times before it ends up as firewood, releasing the previously bound CO2 back into the atmosphere, which impacts climate change. However, hardwood is still too often used only for heating — around 12% of Swiss homes use firewood as a primary fuel source. Innovative ideas for a more sustainable cascade use are therefore needed. One possibility is to equip the natural material with new properties — functionalities — and transform it into magnetic, waterproof, or electricity-generating wood, for instance, to elongate the usage. 

The glowing wood has been achieved due to honey fungus (Desarmillaria tabescens), a pathogen that causes white rot in trees. Some species produce the natural substance luciferin, which is stimulated to glow in a two-stage enzymatic process.

Now, for the first time, the Empa team has succeeded in inducing and controlling the process in the laboratory.

After testing various wood types, Schwarze found balsa wood to be able to hold on to its stiffness and compressive strength after being exposed to the fungus. Through spectroscopy, a scientific technique used to measure and analyze the interaction of light with matter, the researchers observed how the fungus breaks down lignin in the balsa wood samples. 

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.

The biohybrid of fungus and wood develops its maximum luminosity when incubated for three months. The balsa wood samples absorbed eight times their weight in moisture during this time. The enzyme reaction in the wood finally gets triggered when in contact with air. The glow unfolds its full splendor after about ten hours, emitting green light with a wavelength of 560 nanometers, as Empa researcher Giorgia Giovannini from the Biomimetic Membranes and Textiles lab determined during fluorescence spectroscopy analyses.

The fascinating process currently lasts around ten days. "We are now optimizing the laboratory parameters to further increase the luminosity in the future," says Schwarze.