Size-controlled synthesis of near-monodisperse gold ..

ABSTRACT

TECHNICAL SUMMARY

This research project, supported by the Solid State and Materials Chemistry (SSMC) Program in the Division of Materials Research, National Science Foundation aims to study kinetically-controlled syntheses of anisotropic gold nanostructures and their colloidal crystallization in aqueous media. While numerous 3D crystals of spherical particles are known, there are no analogous systems composed of rod-like building blocks. This is because nearly all existing syntheses of nanorods cannot control their length, which often makes them unsuitable for long range 3D crystallization. Seed-mediated synthesis of gold nanorods is a rare example of the reaction producing rods that are fairly well-defined in terms of their length. However, this method is currently non-scalable and cannot offer a sufficient quantity of nanorods to conduct a comprehensive study of their crystallization. This project will develop a route that can scale the synthesis up to four orders of magnitude. The key of the proposed approach is based on uniform amplification of preformed nanorods by reducing residual gold ions on their surface. Preliminary findings show that this goal can be achieved if the rate of reduction is very low, which allows for complete suppression of random nucleation events. Once the large quantities of near-monodisperse nanorods are produced, their crystallization into 3D single crystals will be systematically studied. The project will determine the role of various parameters such as size distribution and purity of rods, their interaction with the underlying substrates, and the rate of solvent evaporation. Of particular importance will be the role of CTAB surfactant that must be present in solution during crystallization. When the best combination of structural and physical variables is identified, periodic arrays of colloidal single crystals will be assembled on lithographically patterned substrates. Measurements of optical, electrical, and mechanical properties of crystals along and perpendicular to the axes of nanorods will be performed in order to assess their direction-dependent vectorial nature.

NON-TECHNICAL SUMMARY

Significant interest in gold nanoparticles with controlled shapes has grown dramatically in the past decade. However, they are often too difficult to make and/or purify. The current commercial price of gold nanorods is more than 7,000 times the price of bulk gold. Therefore, a development of more efficient large-scale synthesis will resolve the issue of their accessibility, which is the main bottleneck of their real-life applications in anticancer therapy, military devices, and invisible cloak technology. Better understanding of mechanisms that govern the assembly of non-spherical particles into large crystals will offer novel types of nanomaterials with direction-dependent properties. The new scientific knowledge generated in the course of this project will be widely disseminated via information sharing techniques and Web2.0 communications. Video materials containing a detailed demonstration of the synthesis of gold nanorods and real-time imaging of 3D crystals by optical and electron microscopy will be posted on the YouTube and Rice University web sites. Of particular importance will be the interactions with science teachers from local middle schools that have a large population of minority students. The PI and his graduate students will use their extensive experience with molecular graphics for 3D visualization of nanostructures and colloidal assemblies in order to create a unique type of activity in Houston public schools that currently collaborate with Rice University. In addition, an exciting outreach activity is planned at the intersection of science and art, which will involve collaborative interactions with the Museum of Fine Arts, Houston.

“ Size Control in the Synthesis of 1 - 6 nm Gold Nanoparticles via ..

Size Controlled Synthesis of Gold Nanoparticles using Photochemically Prepared Seed ..

Gold nanoparticles having prechosen size ranging from 5 to 110 ..

A new synthesis method is presented for the seeded-growth of nearly monodisperse metal nanoparticles ranging from 10 to 100 nm in diameter, both with and without dielectric shells of controlled thickness.

The size-controlled synthesis of ..

Nanomedicines are typically prepared through bottom-up approaches, such as self-assembly of amphiphilic copolymers for the preparation of micelles or vesicles, and nanoprecipitation of hydrophobic polymers for the preparation of NPs. The micellation, vesiclization and nanoprecipitation methods certainly allow for facile preparation of nanomedicines at a large scale. However, the drawbacks of these formulation methods are also obvious; the resulting micelles, vesicles or NPs often have broad particle size distributions, and variable, sometimes uncontrolled drug loading and release profiles. It is also extremely difficult to prepare NPs with narrow or mono-dispersity in size controlled within 100 nm using these conventional technologies. There were even less reports of the in vitro and in vivo properties of NPs with discrete size less than 50 nm., , , , Here, we report the synthesis of drug-silica conjugated NPs (), termed drug-silica nanoconjugates (drug-NCs) and denoted as drug(dye)X (X = particle size in nm), which can be formulated at nearly any size ranging between 20 nm and 200 nm with mono-disperse size distribution (less than 10% coefficient of variation (CV), the ratio of the standard deviation σ to the mean μ of particle size), 10–20% drug loading and controlled drug release profiles. These drug-NCs can be easily prepared on gram scale but still with perfectly controlled size and mono-disperse size distribution. They showed size-dependent cell uptake, biodistribution and tumor penetration capability. By addressing several formulation/development issues (e.g., salt-stability, scalability and lyophilizability, etc.), we developed a potentially clinically applicable drug(dye) delivery nanomedicine platform that can be precisely controlled formulated at any size between 20 and 200 nm on large scale.

28/08/2014 · size-controlled synthesis of monodispersed gold nanoparticles via carbon monoxide gas reduction
Irshad Hussain; Size-Controlled Synthesis of Near-Monodisperse Gold Nanoparticles in the 1−4 nm Range Using Polymeric Stabilizers

controlled synthesis of gold nanoparticles, ..

A seminal early nanoparticle synthesis3a waso fA u55(Ph3P)Cl, whereby the complex [Au(Ph3P)Cl] was reduced with diborane gas. This nanoparticle proved to be difficult to isolate in a pure state and was somewhat unstable. A veryinfluential3bsubsequent synthesis protocol is outlined in Scheme 1, where following phase transfer of a gold salt into an organic medium;using a phasetransfer agent such as tetraoctylammonium bromide;and the addition of an organic thiol, an excess of a strong reducing agent;such as sodium borohydride;is added, with the rapid production of thiolate-protected Au nanoparticles. The parameters of the “Brust synthesis” have been thoroughly explored.3c A major advantage is rough control over the average size of the synthesized particles by the choice of the reduction condition and the gold salt-to-thiol molar ratio used, but even then, in general postsynthesis size fractionation is necessary.

Size-Controlled Synthesis of Near-Monodisperse Gold Nanoparticles in the 1−4 nm Range Using Polymeric Stabilizers

synthesis of monodisperse gold colloids by ..

Highly monodisperse sodium citrate-coated spherical silver nanoparticles (Ag NPs) with controlled sizes ranging from 10 to 200 nm have been synthesized by following a kinetically controlled seeded-growth approach via the reduction of silver nitrate by the combination of two chemical reducing agents: sodium citrate and tannic acid. The use of traces of tannic acid is fundamental in the synthesis of silver seeds, with an unprecedented (nanometric resolution) narrow size distribution that becomes even narrower, by size focusing, during the growth process. The homogeneous growth of Ag seeds is kinetically controlled by adjusting reaction parameters: concentrations of reducing agents, temperature, silver precursor to seed ratio, and pH. This method produces long-term stable aqueous colloidal dispersions of Ag NPs with narrow size distributions, relatively high concentrations (up to 6 × 1012 NPs/mL), and, more important, readily accessible surfaces. This was proved by studying the catalytic properties of as-synthesized Ag NPs using the reduction of Rhodamine B (RhB) by sodium borohydride as a model reaction system. As a result, we show the ability of citrate-stabilized Ag NPs to act as very efficient catalysts for the degradation of RhB while the coating with a polyvinylpyrrolidone (PVP) layer dramatically decreased the reaction rate.

Advanced Materials and Processes II: Size Controlled Synthesis of 2-6 nm Gold Nanoparticles via Controlling Concentration of the Reducing Agent and Temperature

Gold Nanoparticles Size Design and Control by …

In addition to the stirring speed during stage II, the addition speed of NaBH4 (aqueous solution) to reduce Au(I) into clusters also plays an important role in controlling the final cluster size. We have tested that, in the synthesis of Au20(SC2H4Ph)16, if the initial drops of NaBH4 solution (0.44mol/L, 1mL) were added rapidly, the light yellow solution of Au(I) aggregates would rapidly become brown or deep black, and the product would contain more Au24 and Au39/40 clusters, instead of the predominant Au20 as the case of very slow addition of NaBH4 (over a period of approximately 30min) (entry 1, Table). After optimization, we found that adding NaBH4 (0.44mol/L, 1mL, same concentration and amount as the Au20 synthesis) over a period of approximately 15min gave rise to predominant Au24 (under approximately 100rpm stirring condition) or Au39/40 (under approximately 400rpm stirring condition); see entries 2 and 3 of Table. Thus, controlled reduction of Au(I) is very important for size selective formation of Au20, Au24, or Au39/40. The selective formation of Au39/40 over Au24 - which differ only in the stirring speed during stage II (i.e., 400 vs 100rpm, Table) - should be due to the different reaction kinetics in the reduction process of Au(I) species into clusters. In a recent synthetical work on gold/phosphine nanocluster synthesis, Pettibone and Hudgens identified a growth-etching cyclic process that occurs around the most stable cluster species to form monodisperse product [,,]. This size selective growth mechanism provides important information on the gold/phosphine system. The reaction kinetics of the gold/thiol system, however, still needs significant input in order to unravel the details of the kinetic process. Mass spectrometric monitoring of the reaction intermediates would provide valuable information and should be pursued in future work.