Kinetic Control of Microtubule Morphology Obtained by Assembling Gold Nanoparticles on Living Fungal Biotemplates Andressa M. Kubo, † Luiz F. Gorup, † Luciana S. Amaral, ‡ Edson R. Filho, ‡ and Emerson R. Camargo* ,† † LIEC Interdisciplinary Laboratory of Electrochemistry and Ceramics, Department of Chemistry, UFSCar Federal University of Sã o Carlos, Sã o Carlos, Sã o Paulo, 13.565-905, Brazil ‡ Laboratory of Micromolecular Biochemistry of Microorganisms, Department of Chemistry, UFSCar Federal University of Sã o Carlos, Sã o Carlos, Sã o Paulo, 13.565-905, Brazil ABSTRACT: Self-assembly of nanoparticles on living bio- template surfaces is a promising route to fabricate nano- or microstructured materials with high efficiency and efficacy. We used filamentous fungi to fabricate microtubules of gold nanoparticles through a novel approach that consists of isolating the hyphal growth from the nanoparticle media. This improved methodology resulted in better morphological control and faster adsorption kinetics, which reduced the time needed to form homogeneous microtubules and allowed for control of microtubule thickness through successive additions of nanoparticles. Differences in the adsorption rates due to modifications in the chemical identity of colloidal gold nanoparticles indicated the influence of secondary metabolites and growth media in the fungi metabolism, which demonstrated the need to choose not only the fungus biotemplate but also the correct medium to obtain microtubules with superior properties. ■ INTRODUCTION The use of soft templates that combine biological structures and inorganic nanoparticles permits the synthesis and large- scale production of advanced nanostructured hybrid systems with high uniformity and reproducibility. 1-3 For instance, DNA, 4 viruses, 5,6 and microorganisms 7,8 including bacteria 9,10 or fungi 11 present unique structural motifs that are easily and quickly reproduced. In this context, various filamentous fungi have been used as biotemplates to fabricate microwires or microtubules, some of them exhibiting promising optical, electronic, 12 and catalytic properties. 13,14 Due to their facile handling 15-18 and capacity to assembly colloidal nano- particles, 19 these new hybrid materials based on living biotemplates exhibit several potential technological applica- tions. However, there is a lack of information about the best procedures and routing protocols to fabricate such materials. The need to control properties at the nanometer scale resulted in diverse strategies to fabricate and improve the morphology and homogeneity of nanostructured materials. For this reason, it is necessary to understand the system features in and out of equilibrium, 20 especially when the objective is to arrange colloidal nanoparticles on templates. 21,22 Different adsorption kinetic models can be employed to explain the kinetics in liquid-solid systems, 23 but only recently the Lagergren equation (also known as LFO) was used to correlate experimental data from adsorption kinetics of silver nano- particles. 24 In this study, we report an optimized route for the self-organization of colloidal gold nanoparticles on living filamentous fungi to fabricate microtubules of 2-3 μm thick and lengths exceeding a few millimeters. The process involves the synthesis of gold nanoparticles using the citrate method and the growth of Penicillium brasilianum, Aspergillus aculeatus, and Xylaria sp. filamentous fungi biotemplates in different culture media. Gold nanoparticles were added in bottles containing mycelial fungi previously grown in culture medium, and these nanoparticles adhered to the surface of the hyphae, covering it in several layers to form microtubule structures. We evaluated the influence of the three fungal species and culture media on the adsorption time of the particles, tube diameter, tube wall thickness, and length of the wires. Unlike previous studies that focused only on the properties of the final hybrid material, we paid special attention to correlate the adsorption kinetics with the morphological characteristics of the microtubules. ■ RESULTS AND DISCUSSION Self-assembly of nanoparticles using living biotemplates is a promising route to fabricate nano- or microstructured materials with high efficiency and efficacy. 25-29 Many researchers used fungi as templates to build functional hierarchical structures by introducing spores directly into a colloidal suspension of nanoparticles. Although it is the most simple and facile way to promote self-organization of nanoparticles on fungal mycelia, 19 Received: June 24, 2016 Revised: September 10, 2016 Published: September 13, 2016 Article pubs.acs.org/bc © 2016 American Chemical Society 2337 DOI: 10.1021/acs.bioconjchem.6b00340 Bioconjugate Chem. 2016, 27, 2337-2345