The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Chemistry and properties of nanocrystals of different shapes.

PEGylated Nanoparticles for Biological and Pharmaceutical Applications

Nanosized hydrophobic, oleate stabilized silver organosols in various organic solvents are obtained using a solvent exchange method. The silver particles are initially prepared as a hydrosol in the presence of sodium oleate (surfactant). Then a transfer of the colloid to an organic phase is induced by a low concentration of several agents such as orthophosphoric acid, with a transfer efficiency of 50−70%. The hydrophobic colloid is stable and the particles retain their integrity even after the solvent is evaporated and the dried deposit is resuspended in a variety of other solvents. We present the preparation method in detail and characterize the hydrosol and organosol particles by electron microscopy, electrophoresis, and UV−visible extinction spectroscopy. On the basis of IR spectroscopy we discuss the conformation of the surfactant adsorbed on the silver cores and the changes in it as the particles transfer into the organic environment.

Directing Oleate Stabilized Nanosized Silver Colloids into Organic Phases

ZnSe nanoparticles of about 3 nm in size have been prepared by the sonochemical irradiation of an aqueous solution of selenourea and zinc acetate under argon. The ZnSe nanoparticles were characterized using techniques such as transmission electron microscopy, X-ray diffraction, absorption spectroscopy, differential scanning calorimetry, transmission and diffuse reflection spectroscopy, photoluminescence spectroscopy, and energy-dispersive X-ray analysis. The mechanism of the sonochemical irradiation is discussed. This sonochemical method was found to be a general method for the preparation of other selenides as well.

General Sonochemical Method for the Preparation of Nanophasic Selenides: Synthesis of ZnSe Nanoparticles

We study the preparation and capping of silver nanoparticles by several unsaturated long-chain carboxylates UV−visible and FTIR spectroscopy and high-resolution electron microscopy are used to characterize the effect of the chain length, its configuration, and the degree of unsaturation on the size distribution of the nanoparticles Langmuir layers and Langmuir−Blodgett films are used to study the adsorption of these carboxylates on the particles We find that unsaturated carboxylates in the cis configuration are useful stabilizers for the control of particle size and its surface properties

Silver Nanoparticles Capped by Long-Chain Unsaturated Carboxylates

Functionalized reverse micelles are used to control the size and the polydispersity of the metallic and semiconductor particles. The size of the particles can be controlled, either by the amount of water solubilized in the droplets, or by the solvent used to form reverse micelles, or by adding macrocyle molecules.

Synthesis “in situ” of nanoparticles in reverse micelles

Functionalized reverse micelles are used to control the size of silver sulfide, Ag2S, nanosized particles. The size of the crystallites varies linearly with the water content from 2 to 10 nm. The particles have been coated by dodecanethiol and extracted from micelles. The size of the particles dispersed in heptane has bene determined by SAXS experiments and compared to those obtained by TEM. A good agreement between these two technics is obtained. A drop of the particles previously dispersed in heptane is dried on a carbon grill. A network of the particles forming monolayers of crystallites in a hexagonal distribution appears.

J. Cizeron

Papers

Synthesis “in situ” of nanoparticles in reverse micelles

Synthesis “in situ” in reverse micelles of silver sulfide semiconductors