A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Nanotechnology

Thesis (Ph.D.) - Asian Institute of Technology, 2013

Aligned and structured point-to-point biomimetic microwires growth was attempted by controlled integration of microbial tropism and self-organization of metallic nanoparticles (glutamate capped gold colloids) on living template of Aspergillus niger (A. niger) hyphae. Ajinomoto® (MSG) served as the stabilizing and reducing agent for gold colloid nanoparticles and also acted as a source of nutrients for the growth of fungal hyphae. Because the tips of growing fungi are sensitive to surrounding physical or chemical environmental changes, fabrication of polarized micro-assemblies were made possible by the application of various tropic factors like visible light, nutrient flow, temperature, relative humidity (rH) as well as physical contact and gravity. Gold microwires fabricated in this way had length beyond 1mm and of about 1 to 2 om diameter. These wires showed the maximum divergence of 40⁰-50⁰ from the light path irrespective of different illuminated colour and displayed wide variation in dimension and morphology. Fungal growth in terms of hyphal length, branched intensity as well as re-orientation was analyzed statistically. Optical modeling was done successfully to visualize the phototropic response of fungal templated gold microwires towards different wavelengths. Whereas, thigmotropism and gravisensing did not show demonstrable patterning of templated wires under the same conditions. To the best of our knowledge, this is first time that the application of tropism and self-organization on living entities were used in conjunction to pattern the mesh of ultrathin, small, and robust microwires having high surface area for potential applications in sensing, catalysis, electronic and optical industry.