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10/9/10

Carbon encapsulation to increase gold nanoparticle stability

Gold nanoparticle has limitations in biological and chemical nanotechnology applications due to the problems of stability and their tendency for non-specific binding. To overcome thIs problem carbon nanoshells are used to encapsulate gold and other noble metal particles. A graphene-like carbon shell is ideal for surface passivation because it is nonreactive with the metallic surface, provides unsurpassed stability and possesses a convenient handle for functionalization.
Fabrication of encapsulation
The research in graphene or carbon shell growth has been largely focused on utilizing transition metals, such as iron, as catalysts. With regard to gold nanoparticles there has been only limited research. Previously, carbon shells were grown on gold nanoparticles that were dispersed onto a lacey carbon transmission electron microscope grid and irradiated with a high intensity electron beam in a TEM at high temperatures. Their size , however is limited to the size of the TEM grid which is very small and can not be utilized for practical applications but can be stable in biological media.
New method
A fabrication method to encapsulate gold nanoparticles is to utilise surface oxidized gold nanoparticles as catalysts for the growth of the carbon shells with well-controlled thickness employing a chemical vapor deposition (CVD) process.By this method considerable quantity of materials can be produced in few hours.A new method uses a large area silicon substrate for gold nanoparticle deposition and carbon shell growth and to produce large sample size for different applications where nanoparticle stability is of concern. By varying the CVD growth conditions, the thickness of the carbon shell can be controlled, but, prolonged growth durations of more than four hours ruptures the carbon shells and dissociates from the gold core. Main applications are in bioanalysis and sensing as the carbon surface is functionalized and the optical properties of the retained gold nanoparticles can also be used in many optical applications and sensing but the integration into complex chemical and biological analysis and sensing devices is a challenge.
Use of gold nanoparticles
Gold nanoparticles have emerged as attractive nanomaterials for biological and biomedical applications because of their physical and chemical properties. The gold core is inert and essentially non-toxic to cells. The particles absorb and resonantly scatter visible and near-infrared light upon excitation of their surface plasmon oscillation. The plasmon resonance band can be tuned over a wide spectral range by changing intrinsic parameters such as the material (bi-metallic or hybrid particles), the size, or the shape (sphere, rod, cube, triangle, cage, etc.). The light-scattering signal is intense and much brighter than chemical fluorophores and does not photobleach or blink. This constitutes an advantage for their applications in single molecule imaging, where the use of dyes, fluorophores, or quantum dots is limited by low signal intensities, complex blinking phenomena, and photobleaching. For particles below 30 nm, the absorption becomes dominant over scattering and can be used for detection by photothermal microscopy.
Functionalisation
Gold nanoparticles with varying core size are prepared by the reduction of gold salts in the presence of stabilizing agents to prevent nanoparticle agglomeration and control growth. Particle suspensions are also commercially available. Furthermore, gold nanoparticles can be easily functionalized by anchoring thiol linkers in their monolayers. A wide variety of functional bionanoconjugates has been obtained, including nanoparticles modified with peptides, proteins, antibodies, oligosaccharides, and nucleic acids. This allows the nanomaterials to act as multifunctional platforms for both therapeutic and diagnostic purposes.
Use of functionalized gold nanoparticles
The use of functionalized gold nanoparticles for biological and biomedical applications includes bio-imaging, single molecule tracking, biosensing, drug delivery, transfection, and diagnostic. For example, through proper functionalization, the particles can be engineered to accumulate preferentially in tumor cells using targeting ligands, providing a tool for cancer diagnosis and gene therapy. Sensor arrays have been developed to differentiate normal, cancerous, and metastatic cells using the fluorescence quenching properties of gold nanoparticles. The interactions and fate of a broad range of functionalized nanoparticles is currently under investigation in a wide diversity of biological models, ranging from whole organisms to tissues to cells in culture, and also to yeast and prokaryote bacteria.
Removing pollutants
Gold nanoparticles in the form of spherical Colloids, polycrystalline at concentrations of 0.05 mg/ml are excellent for functionalization and are used in a multitude of applications. The gold can be deposited onto manganese oxide by means of vacuum-UV laser ablation and when irradiated, it dislodges gold particles through evaporation. These gold particles have unusually high energy, and allow them to drive relatively deep into the surface of the manganese oxide. This effectively removes volatile organic compounds as well as nitrogen and sulfur oxides from air at room temperature.Gold clusters have been shown to exhibit intrinsic fluorescence that varies with the size of the cluster. Intrinsically fluorescent gold nanoclusters (less than 4 nm.size) display less photo bleaching than organic fluorophores.

1 Responses to “Carbon encapsulation to increase gold nanoparticle stability”

Anonymous said...
July 16, 2012 at 6:37 PM

can we compress other carbon encapslated elementals that are relative to the golds existance in a specific seqence to the deposit of the ore.and keep adding and compressing the shell orbital seqence until implosive events scince the earth has just imploded an iron core. what ever that means. and the wastefield anomolys at hanford and the world? has unstabile imploded cylindricals.that is the earths core image.the hour glass shape is core image in real time.its most likely imploding a highly refined metal partical on a subatomical level.then build up to atomical then large partical building.like venus is organic protein folding.analytical.


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