Metallization of biologically inspired silica nanotubes

a r t i c l e i n f o The desire and need for various types of nanostructures have been met with challenges of feasibility, reproducibility, and long fabrication time. To work towards improved bottom-up methods of nano-fabrication, we use bacterial flagella as bio-templates for fabricating silica-mineralized nanotubes, which are ideal for the formation of metal nanoparticles or metal oxide nanoparticles. In this study, we show that silica nanotubes formed from flagella templates can be coated with gold, palladium, and iron oxide nanoparticles under mild aqueous conditions. The process was accomplished through reactions including reductive metallization or oxidative hydrolysis. Morphology and chemical composition were analyzed by transmission electron microscopy and energy dispersive X-ray spectroscopy, respectively. The results from these studies provide evidence for the complete coating of silica nanotubes with metal nanoparticles using a simple and fast procedure. There is considerable interest in the synthesis of inorganic–organic nanotubes using bio-materials for the utilization of micro-or nanoscale devices. Biologically derived materials are claimed to be more advantageous over other artificial materials due to the reputed simplicity of chemically manipulating the synthesis and mass production of such materials. Recently, we demonstrated that bacterial flagella can be used as potential bio-templates because of their unique features such as small diameter (inner diameter is 2 nm and outer diameter is approximately 20 nm) and long length, their unique tubular structure, and their robustness in harsh conditions [1,2]. The flagella-template allowed the generation of silica-mineralized flagella nanotubes (SMFNs) in an efficient manner by a well-controlled hydrolysis and condensation reaction. Moreover, the synthesized silica on flagella templates successfully formed uniform layers with a controllable thickness in various sizes while maintaining the structure and function of the flagella [1]. Silica nanomaterials in particular are popular because, compared with carbon, production is cheaper and can be conveniently produced in large quantities and chemically functionalized [3]. Specifically, the ease of which one can functionalize silicon's surface makes it a very promising and useful scaffold for metallization with control over morphology and composition using metal nanoparticles or metal oxides [4,5]. Metallic nanoparticles possess unique optical and electrical properties making them extremely useful in broad range of fields. In particular, gold (Au) nanoparticles have attracted significant attention for the applications of photothermal therapy and optical systems because of their plasmonic property [6,7]. Palladium (Pd) nanoparticles are also of great interest in electronics and catalysis due to desirable electrical properties …