Nanowires: Synthesis, fluorescence functionalization, and biological applications

The introduction describes recent advances in nanomaterials fabrication that have led to the synthesis of high aspect ratio particles on nanometer length scales. The elongated structure of these materials often results in inherent chemical, electrical, magnetic, and optical anisotropies that can be exploited for interactions with cells and biomolecules in fundamentally new ways. Recently developed procedures for the fabrication of nanorods, nanowires, and nanotubes are briefly described. Recent literature reports that describe the use of high aspect ratio nanoparticles for biological sensing, separations, and gene delivery are summarized. The recent discovery of single nanowire field-effect transistors may revolutionize biological sensing and yield extremely low detection limits. Separations technology with chemically modifiable nanotube membranes and with magnetic nanowires that can be tailored to selectively interact with molecules of interest is also summarized. Other areas of biotechnology that have been improved by the integration of high aspect ratio nanoparticles are also covered.; Gold, nickel, and two-segment nickel-gold nanowires have been synthesized by electrodeposition into alumina templates. The nanowires had 350 nm diameters and were typically 12--22 mum in length. The nanowires were removed from the templates and were functionalized with organic molecules. Nickel nanowires have been functionalized with 8,13-bis(1-hydroxyethyl)-3,7,12,17-tetramethyl-21H,23H-porphine-2,18-dipropionic acid (HemIX). Adsorption isotherms were constructed for the binding of HemIX to nickel nanowires in ethanol solution at 298 K. Adduct formation constants of 9 +/- 5 x 106 M-1 and limiting surface coverages of 8 x 10-10 mol/cm2 selectively functionalized with thiols bound selectively to gold and carboxylic acids bound to nickel. This functionalization was optimized for selectivity and stability of the nanowire-molecule linkages. Fluorescence microscopy was used to demonstrate the covalent binding of thiol-terminated porphyrins to Au nanowires.; Nanowires with free amino or thiol functional groups were reacted with activated dyes to yield amide, thiourea, and thioether covalent linkages that were quantified by fluorescence microscopy. These reactions with two-segment nickel-gold nanowires produced materials that emitted light only on one segment of the nanowire or emitted light of different colors on each segment.; Metal oxide nanowires were synthesized by electrochemical deposition of TiO2, iron oxide, and ZnO. ZnO and TiO2 nanowires were also synthesized via a sol-gel procedure. Multi-segment nanowires that contain a metal oxide segment were synthesized by sequential electrochemical deposition.; Nickel nanowires response to magnetic fields were observed using video microscopy. In viscous solvents, magnetic fields can be used to orient the nanowires; in mobile solvents, the nanowires form chains in a head-to-tail configuration when a small magnetic field was applied. The dynamics for chain formation have been quantitatively modeled. The results demonstrate a new approach for assembling nanowires. Nickel nanowires were then bound to NIH-3T3 mouse fibroblasts and magnetic fields used for cellular manipulation. The dynamics for chain formation of nanowires bound to mammalian cells has been qualitatively demonstrated.