Fungi Culture Department in the IC Factory

Agriculture not only provides us with foods, but also raw materials for industrial products such as baskets, cloths, etc., depending on how sophisticated the technology is involved. This status of agriculture was somewhat limited in the last century by the development of traditional petrol-based chemical engineering and IT industry, where plastics and metal derivatives became more essential. Now we have realized the benefits of agriculture as a recyclable resource and tried to depend more than before on it. Poly(lactic acid) is one of the successful steps to base the plastics industry less on exhausting petroleum resource. But how can IT industry be more recyclable, or green in its products besides its process? Maybe we can make use of fungi.

Fungi and other micro-organisms including viruses and bacteria grow into unique and structurally interesting forms that have been used by many researchers as templates for the self-organization of inorganic materials with the aim of realizing functional macrostructures. Of which, coating nanoparticles onto the hyphae of a filamentous fungus provides a product with diameters of the order of a few micrometers ad lengths varying from tens of micrometers to a few millimeters. Immediate applications as circuit components, high-surface-area sensors, or optically active structures, depending on the functionality of the nanoparticles, can thus be realized. A typical work of this field is a recent communication on Adv. Mater. (2007, 19, 77-81. DOI: 10.1002/adma.200600911.) by J. Dutta and co-workers. They grew fungi in gold nanoparticle solution, the stabilizers of which are also nitrogen and carbon sources, or nutrition, of the fungi. Therefore the growing fungi gradually used up the stabilizers, causing the gold nanoparticles to agglomerate and accumulate on the hyphal walls, which exhibits the optical properties of bulk gold, a process the authors called 'nutrition-driven assembly'. Further experiments showed that only an actively growing fungus can assemble the colloidal nanoparticles on its hyphae, and a weak ligand-particle interaction is also essential for triggering the self-assembly process.

The resultant bright golden color in reflected light indicates that the gold particles have formed 'hard agglomerates', leading to the dominance of bulk gold properties. So the authors performed preliminary electrical measurements on a bundle of the microwires grew from the fungi. The average resistance obtained from the slope of the current-voltage (I-V) plot was found to be ca. 6.7Ω. By drying the product under supercritical extraction, the inner water-based materials of the fungi dry out and shrink easily, while the desiccated cell wall remain stuck to the inner surface of the resultant tubular assembly of gold nanoparticles. With post-fabrication treatment, this process could lead to a simple technique for achieving freestanding gold microtubules.

This technique can possibly be extended to other metal or metal oxide nanoparticles and micro-organisms with various micro-morphologies. In principle, any micro-organism that can survive on simple nutrients can act as templates, while the weak ligand-particle interaction and the consequent sensitivity to the ionic content in the dispersant medium can drive the organized agglomeration. In the future, maybe we will have a fungi or amoeba culturing department in every integrated circuit factory.