Iron–Gold Barcode Nanowires

Abstract

Nanowires are a focus of research interests as one-dimensional nanosystems and promise exciting applications in nanotechnology, ranging from nanoelectronic devices to cell separation and magnetic labeling in biomedicine. Avariety of methods have been devised to prepare them from magnetic, semiconductor, inorganic, organic, polymer, metallic, and dielectric materials to provide nanowires with novel optical, electrical, catalytic, and magnetic properties. Multilayered or barcode arrangements of nanowires which incorporate different material components are a special case as a result of their spatial arraying, multiple functionalities, and enhanced properties in comparison to those of their single-component counterparts. For instance, Co–Cu barcode nanowires were explored for their high magnetoresistance compared to that of the well-studied thin films, 17] while the coding of magnetic and optical properties in a single wire was targeted for the separation, detection, and transport of cells. Interested in the transport properties and potential applications of nanowires in nanodevices and biomedicine, we have investigated magnetic nanowires by electrodeposition. For biomedical purposes, however, two issues have to be addressed for the implementation of such nanowires, namely surface modification and biocompatibility. In this respect, the synthesis of iron–gold (Fe–Au) nanowires is appealing not only in terms of magnetic properties but also with respect to biological compatibility. On one hand, iron is favored as it is unique in the field of magnetic materials owing to its high magnetization and physicochemical potentiality. It can be easily converted into oxides, which have been thoroughly studied in the form of magnetic nanoparticles in the biomedical field for their magnetic properties and exceptional biocompatibility. On the other hand, gold is a wellestablished material that displays attractive optical properties, biological compatibility, catalytic activity, and excellent surface effects. Thus, it was anticipated that the integration of these two materials into a one-dimensional barcode arrangement on the nanoscale would produce a new nanostructured material that retains the optical and magnetic properties of the respective components, offering synergistically enhanced performance and functionalities which go beyond those of the individual components. Herein, we report the synthesis and characterization of such a kind of multifunctional magnetic–optical Fe–Au barcode nanostructures, that is, nanowires consisting of alternative Fe magnetic and Au optical segments. The Fe–Au barcode nanowires were constructed using anodic alumina oxide (AAO) templates by pulse electrodeposition thus forming iron and gold segments alternatively in a single bath under desired pulse current densities (e.g. 10 mAcm 2 and 0.5 mAcm ) with regulated pulse durations to control the respective segmental lengths (see Experimental Section). The selection of a current density to electrodeposit Fe or Au was based on the evaluation of the composition versus current density profile (Figure 1a), which was acquired from the analysis of the samples each obtained at a given constant current density, by inductively coupled