Gold nanotubes

Zhou, J. and Dong, J. (2007) Vibrational properties of single-walled gold nanotubes from first principles. Physical Review B Condensed Matter, 75, 155423-1-155423-7. 

Yang, X. and Dong, J. (2005) Geometrical and electronic structures of the (5, 3) single-walled gold nanotube from first-principles calculations. Physical Review B -Condensed Matter, 71,233403-1-233403-4. 

Metal nanotube membranes with electrochemically suitable ion-transport selectivity, which can be reversibly switched between cation-permeable and anion-permselective states, have been reported. These membranes can be viewed as universal ion-exchange membranes. Gold nanotube molecular filtration membranes have been made for the separation of small molecules (< 400 Da) on the basis of molecular size, eg. separation of pyridine from quinine (Jirage and Martin, 1999). 

Whereas the previous example relies on a series of channels etched into the membrane, typical single-channel stochastic sensors can be created in a closely related way.91 For such sensors, usually one protein (e.g., a-hemolysin) is introduced into a lipid bilayer. However, the problem here is that lipid bilayers are rather fragile objects. As an alternative, Martin and coworkers embedded a single gold nanotube... 

Gold nanotubes have been made by electroless plating within the 220 nm diameter pores of a polycarbonate membrane.66... 

We now describe synthetic membranes in which the molecular-recognition chemistry used to accomplish selective-permeation is DNA hybridization. These membranes contain template-synthesized gold nanotubes with inside diameter of 12 nm, and a transporter DNA-hairpin molecule is attached to the inside walls of these nanotubes. These DNA-functionalized nanotube membranes selectively recognize and transport the DNA strand that is complementary to the transporter strand relative to DNA strands that are not complementary to the transporter. Under optimal conditions, single-base mismatch transport selectivity is obtained. 

The gold nanotube membranes were prepared via the template synthesis [21,22] method by electroless deposition of gold along the pore walls of a polycarbonate template membrane [19,43]. The template was a commercially available filter (Osmonics), 6 p.m thick, with cylindrical 30 nm diameter pores and 6 x 10 pores per square centimeters of membrane surface area. 

FIGURE 43.8 Gold nanotube synthesized by using a50 nm polycarbonate membrane template. (Reprinted from Shao, P., Ji, G., and Chen, P., J. Membr. Set, 255, 1, 2005. With permission from Elsevier.)... 

Nevertheless, unsupported powdered gold (mean diameter, 76 nm) proved to be active for CO oxidation [138,139], and so did naked gold [140] and gold nanotubes [141] under mild conditions. In addition, investigations by Flytzani-Stephanopoulos and co-workers [142-144] on the water-gas shift (WGS) reaction (see Sect. 6.4.1) have challenged the idea that gold nanoparticles are essential, but these investigators have not exhaustively proved the complete absence of Au(0). 

Siwy et al. demonstrated the utility of a single conically shaped gold nanotube that was embedded in a mechanically and chemically robust polymeric membrane [142]. They reported biofunctionalized conical Au nanotubes, which are potentially useful for obtaining highly sensitive and selective protein biosensors. So et al. introduced a single walled carbon nanotube field effect transistor (SWNT-FET) combined with aptamers as an alternative to the corresponding antibody [143]. 

TCGCG3 (30-mer). - In all of the experiments described here, the conically shaped gold nanotube was left embedded within the polycarbonate membrane. However, in order to prove that this nanotube is, indeed, conical, the membrane was dissolved away, and the liberated nanotubes were imaged via electron microscopy (Figure 20.24c). 

I-V curves for these artificial ion channels were obtained by mounting the membrane sample between the two halves of a U-tube conductivity cell. Each half-cell was filled with 5 mL of a 10 mM pH = 7 phosphate buffer that was also 100 mM in KCl. A Ag/AgCl reference electrode was inserted into each half-cell solution, and a Keithley Instruments 6487 picoammeter/voltage source was used to apply the desired transmembrane potential and measure the resulting ionic current flowing through the gold nanotube. 

Although this chapter is limited to electrodeposition of semiconductors, it is only fair to mention, even if briefly, some examples of electrodeposition of metal nanostructures. This is important because the principles and techniques used in electrodepositing metals are essentially the same as those used for depositing semiconductors - the main difference is that almost all studies on electrodeposition of nanocrystalline semiconductors involve compound semiconductors, with the added comphcations this entails. Examples include pulsed electrodeposition of metal multilayers [1, 2], porous membrane-templated electrodeposition of gold nanotubes [3], and Ni nanowires [4]. 

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