Showing papers by "Sara E. Skrabalak published in 2007"

Facile synthesis of Ag nanocubes and Au nanocages

Abstract: This protocol describes a method for the synthesis of Ag nanocubes and their subsequent conversion into Au nanocages via the galvanic replacement reaction. The Ag nanocubes are prepared by a rapid (reaction time < 15 min), sulfide-mediated polyol method in which Ag(I) is reduced to Ag(0) by ethylene glycol in the presence of poly(vinyl pyrrolidone) (PVP) and a trace amount of Na2S. When the concentration of Ag atoms reaches supersaturation, they agglomerate to form seeds that then grow into Ag nanostructures. The presence of both PVP and Na2S facilitate the formation of nanocubes. With this method, Ag nanocubes can be prepared and isolated for use within approximately 3 h. The Ag nanocubes can then serve as sacrificial templates for the preparation of Au nanocages, with a method for their preparation also described herein. The procedure for Au nanocage preparation and isolation requires approximately 5 h.

Gold Nanocages for Biomedical Applications

Abstract: Nanostructured materials provide a promising platform for early cancer detection and treatment. Here we highlight recent advances in the synthesis and use of Au nanocages for such biomedical applications. Gold nanocages represent a novel class of nanostructures, which can be prepared via a remarkably simple route based on the galvanic replacement reaction between Ag nanocubes and HAuCl4. The Au nanocages have a tunable surface plasmon resonance peak that extends into the near-infrared, where the optical attenuation caused by blood and soft tissue is essentially negligible. They are also biocompatible and present a well-established surface for easy functionalization. We have tailored the scattering and absorption cross-sections of Au nanocages for use in optical coherence tomography and photothermal treatment, respectively. Our preliminary studies show greatly improved spectroscopic image contrast for tissue phantoms containing Au nanocages. Our most recent results also demonstrate the photothermal destruction of breast cancer cells in vitro by using immuno-targeted Au nanocages as an effective photo-thermal transducer. These experiments suggest that Au nanocages may be a new class of nanometer-sized agents for cancer diagnosis and therapy.

Photoacoustic tomography of a rat cerebral cortex in vivo with au nanocages as an optical contrast agent.

Abstract: Poly(ethylene glycol)-coated Au nanocages have been evaluated as a potential near-infrared (NIR) contrast agent for photoacoustic tomography (PAT). Previously, Au nanoshells were found to be an effective NIR contrast agent for PAT; however, Au nanocages with their more compact sizes ( 100 nm for Au nanoshells) and larger optical absorption cross sections should be better suited for in vivo applications. We sequentially injected Au nanocages into the circulatory system of a rat in three administrations and in vivo PAT was conducted immediately prior to the first injection and continued until 5 h after the final injection. A gradual enhancement of the optical absorption in the cerebral cortex, by up to 81%, was observed over the course of the experiment.

Porous Carbon Supports Prepared by Ultrasonic Spray Pyrolysis for Direct Methanol Fuel Cell Electrodes

Abstract: Carbon powders composed of porous micrometer-sized spheres were synthesized from simple organic salt precursors using ultrasonic spray pyrolysis (USP). These materials were tested as catalyst supports for a direct methanol fuel cell (DMFC) catalyst and as pore formers in a membrane electrode assembly (MEA). The effect of these materials on unit cell performance was evaluated and compared to traditional Vulcan XC-72 carbon nanoparticle powder. USP provides a simple and facile way to prepare porous carbons with various morphologies and pore sizes. In exploring these new morphologies of carbon, two types of micrometer-sized spherical porous carbons were tested as pore-forming additives for both the anode catalyst (i.e., PtRu/C for methanol oxidation) and the cathode catalyst (i.e., Pt/C for O2 reduction). The anode catalyst mixture of PtRu/Vulcan and PtRu/PC-I (weight ratio 2:1, 33 wt % PC-I) showed the highest performance improvement and is attributed to the synergic effect of two carbons (PC-I and Vulcan X...

Galvanic replacement reaction: A simple and powerful route to hollow and porous metal nanostructures

Abstract: Galvanic replacement reaction provides a remarkably simple and versatile route to metal nanostructures with controllable hollow interiors and porous walls. The key step of this process involves the replacement reaction between a suspension of nanoscale metal templates and a salt precursor containing a relatively less active metal. This method has been successfully applied to prepare gold-based hollow nanostructures with a wide range of different morphologies, including cubic nanoboxes, cubic nanocages, triangular nanorings, prism-shaped nanoboxes, single-walled nanotubes, and multiple-walled nanoshells or nanotubes. In addition to gold, hollow platinum and palladium nanostructures have also been prepared by using appropriate salt precursors for the replacement reaction. These hollow and porous metal nanostructures show intriguing optical and mechanical properties, with their surface plasmon resonance peaks tunable from the visible to the near-infrared region. These materials are expected to find a...

Carbon Powders Prepared by Ultrasonic Spray Pyrolysis of Substituted Alkali Benzoates

Abstract: Ultrasonic spray pyrolysis (USP) has been used to prepare carbon spheres from aqueous solutions of substituted alkali benzoate salts. The size of the carbon spheres produced during USP can easily be controlled simply by changing the concentration of the precursor solution. Both the cation and the ring substituents of a given precursor influence product morphology, which ranges from solid spheres to hollow bowls to porous spheres. Thermogravimetic analysis of the various precursors suggests that the relative temperature of decomposition steps releasing gas explain these observed morphology differences.

Porous Materials Prepared by Ultrasonic Spray Pyrolysis

Abstract: Ultrasonic spray pyrolysis (USP) is a simple aerosol synthetic technique. A schematic of a laboratory-scale USP setup is shown in Figure 1A, and a photograph of the atomization chamber is shown in Figure 1B. The base of a household humidifier, equipped with an ultrasonic transducer, provides the energy necessary for liquid atomization. A fine mist of precursor droplets (diameters < 5 μm) is carried by a gas into a furnace where solvent evaporation and precursor decomposition occurs. Product particles are then collected in bubblers positioned at the end of the furnace; byproducts are either dissolved in the collection media or flushed out of the system by carrier gas. Using this technique, both fine powders and nanoparticles have been produced. Precursor droplets also can be deposited onto heated substrates, allowing for the production of films. 7 There are numerous examples of metal oxide and metal chalcogenide production using USP, 2 and shown in Figure 1C is a representative scanning electron micrograph (SEM) of MoS2 particles prepared by traditional USP.