Published: April 1st, 2013
Solution-suspendable gold nanotubes with controlled dimensions can be synthesized by electrochemical deposition in porous anodic aluminum oxide (AAO) membranes using a hydrophobic polymer core. Gold nanotubes and nanotube arrays hold promise for applications in plasmonic biosensing, surface-enhanced Raman spectroscopy, photo-thermal heating, ionic and molecular transport, microfluidics, catalysis and electrochemical sensing.
A nearly parallel array of pores can be produced by anodizing aluminum foils in acidic environments1, 2. Applications of anodic aluminum oxide (AAO) membranes have been under development since the 1990's and have become a common method to template the synthesis of high aspect ratio nanostructures, mostly by electrochemical growth or pore-wetting. Recently, these membranes have become commercially available in a wide range of pore sizes and densities, leading to an extensive library of functional nanostructures being synthesized from AAO membranes. These include composite nanorods, nanowires and nanotubes made of metals, inorganic materials or polymers 3-10. Nanoporous membranes have been used to synthesize nanoparticle and nanotube arrays that perform well as refractive index sensors, plasmonic biosensors, or surface enhanced Raman spectroscopy (SERS) substrates 11-16, as well as a wide range of other fields such as photo-thermal heating 17, permselective transport 18, 19, catalysis 20, microfluidics 21, and electrochemical sensing 22, 23. Here, we report a novel procedure to prepare gold nanotubes in AAO membranes. Hollow nanostructures have potential application in plasmonic and SERS sensing, and we anticipate these gold nanotubes will allow for high sensitivity and strong plasmon signals, arising from decreased material dampening 15.
When their dimensions approach the penetration depth of light (~50 nm; the nanoscale), noble metals, and most importantly gold, exhibit exquisite size, shape and environment dependent optical properties 24, 25. On this scale, direct illumination causes a coherent oscillation of conduction electrons known as the surface plasmon resonance (SPR). SPR is highly dependent on nanostructure size, shape, and the dielectric properties of the surrounding medium. There is great interest in characterizing SPR properties in new materials, as SPR-based devices are emerging for use in sub-wavelength optics, SERS substrates, and ultra-sensitive optical sensors 11-16, ....
1. Forming the Silver Working Electrode
After each step, one can visibly determine whether or not the synthesis is successful by observing the color of the membrane. After copper deposition (step 2.3) the template will appear purple. During nickel deposition (step 2.5) the template will slowly turn black. After the polymer deposition (step 3.3) the template should appear darker purple/black and more glossy (Figure 2). Typical chronoapmerograms of successful polymer and gold are included (Figure 3). During the final etching ste.......
Template directed synthesis of nanorods in AAO membranes has become increasingly popular, however syntheses of nanorods tend to be very sensitive towards minor changes in material and synthesis conditions. Here, a comprehensive understanding of the advantages and limitations of using AAO membranes is outlined, as well as a general guideline for using AAO membranes for electrochemical synthesis of nanostructures.
When purchasing AAO membranes, there are two general types available: asymmetric a.......
This work was supported by the University of Toronto, the Natural Sciences and Engineering Research Council of Canada, the Canadian Foundation for Innovation, and the Ontario Research Fund. DSS thanks the Ontario Ministry for an Early Researcher Award.....
|UniKera Standard Membrane
|Synkera Technologies Inc.
|Anodic aluminum oxide membranes are available from synkera in various pore sizes ranging from 13 - 150 nm, and thicknesses from 50 to 100 μm. We use the 50 μm ones. They are symmetric, meaning the pore size is uniform from top to bottom.
|Anopore Inorganic Membranes
|13 mm diameter, 200 nm pore size. These membranes are very fragile. The pore diameters are not uniform throughout, so it is important to always use the bottom of the membrane as the working electrode
|Silver Pellets %99.99
|Kurt J. Lesker
|Copper(II) sulfate pentahydrate
|Caution: corrosive liquid
|Hydrogen peroxide (30%)
|Caution: oxidizing liquid
|Caution: corrosive fuming liquid
|Caution: caustic powder
|Watts Nickel Pure
|Product is no longer available from Technic inc., however other commercial nickelplating solutions will work.
|Contains cyanide, do not acidify
|Boron trifluoride diethyl etherate
|Must be stored and used under inert atmosphere
|EC Epsilon potentiostat/galvanostat
|BASi (Bioanalytical Systems, Inc.)
|Reference electrodes and platinum wires were included with the potentiostat, and replacements can be purchaes from BASi http://www.basinc.com/products/ec/epsilon/features.html
|Cary 5000 UV-Vis-NIR spectrophotometer
|Branson 2510 Ultrasonic Cleaner
|Z244810 (From Sigma Aldrich)
|Covap 2 thermal evaporator
|Millipore Synergy water purification system
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