Visible-Light-Induced Directed Gold Microwires by Self-Organization of Nanoparticles on Aspergillus Niger

A directional point-to-point growth of microwires of gold nanoparticles (AuNPs) self-organized on Aspergillus niger (A. niger) templates by utilizing positive phototropic fungal response to different spectral ranges of visible light is reported. A. niger serves as a living template for the self-organization of monosodium glutamate (MSG) capped gold colloids under controlled nutrient trigger and appropriate light, temperature, and humidity conditions. The experimental results show that control of these parameters eliminates the need for any microchannels for the directional growth of microwires. The growth rate of fungal hyphae increases exponentially under light illumination compared to its growth in the dark under similar conditions. White light is found to be most suitable to trigger the directional growth. Gold microwires of about 1 to 2 m diameter and length exceeding 1 mm are grown within a week with a maximum divergence of 40-50 degrees from the light path regardless of the wavelength of the light irradiation. Phototropic response of fungi has been investigated intensively over the last three decades, but this is the first report on the collective use of microbial tropism and directed biomimetic self-organization of metallic nanoparticles on living organisms.