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.

Synthesis and surface engineering of iron oxide nanoparticles for biomedical applications

This review focuses on the synthesis, protection, functionalization, and application of magnetic nanoparticles, as well as the magnetic properties of nanostructured systems. Substantial progress in the size and shape control of magnetic nanoparticles has been made by developing methods such as co-precipitation, thermal decomposition and/or reduction, micelle synthesis, and hydrothermal synthesis. A major challenge still is protection against corrosion, and therefore suitable protection strategies will be emphasized, for example, surfactant/polymer coating, silica coating and carbon coating of magnetic nanoparticles or embedding them in a matrix/support. Properly protected magnetic nanoparticles can be used as building blocks for the fabrication of various functional systems, and their application in catalysis and biotechnology will be briefly reviewed. Finally, some future trends and perspectives in these research areas will be outlined.

Magnetic nanoparticles: Synthesis, protection, functionalization, and application

1. Introduction 20642. Synthesis of Magnetic Nanoparticles 20662.1. Classical Synthesis by Coprecipitation 20662.2. Reactions in Constrained Environments 20682.3. Hydrothermal and High-TemperatureReactions20692.4. Sol-Gel Reactions 20702.5. Polyol Methods 20712.6. Flow Injection Syntheses 20712.7. Electrochemical Methods 20712.8. Aerosol/Vapor Methods 20712.9. Sonolysis 20723. Stabilization of Magnetic Particles 20723.1. Monomeric Stabilizers 20723.1.1. Carboxylates 20733.1.2. Phosphates 20733.2. Inorganic Materials 20733.2.1. Silica 20733.2.2. Gold 20743.3. Polymer Stabilizers 20743.3.1. Dextran 20743.3.2. Polyethylene Glycol (PEG) 20753.3.3. Polyvinyl Alcohol (PVA) 20753.3.4. Alginate 20753.3.5. Chitosan 20753.3.6. Other Polymers 20753.4. Other Strategies for Stabilization 20764. Methods of Vectorization of the Particles 20765. Structural and Physicochemical Characterization 20785.1. Size, Polydispersity, Shape, and SurfaceCharacterization20795.2. Structure of Ferro- or FerrimagneticNanoparticles20805.2.1. Ferro- and Ferrimagnetic Nanoparticles 20805.3. Use of Nanoparticles as Contrast Agents forMRI20825.3.1. High Anisotropy Model 20845.3.2. Small Crystal and Low Anisotropy EnergyLimit20855.3.3. Practical Interests of Magnetic NuclearRelaxation for the Characterization ofSuperparamagnetic Colloid20855.3.4. Relaxation of Agglomerated Systems 20856. Applications 20866.1. MRI: Cellular Labeling, Molecular Imaging(Inﬂammation, Apoptose, etc.)20866.2.

Magnetic Iron Oxide Nanoparticles: Synthesis, Stabilization, Vectorization, Physicochemical Characterizations, and Biological Applications

Nanocrystals are fundamental to modern science and technology. Mastery over the shape of a nanocrystal enables control of its properties and enhancement of its usefulness for a given application. Our aim is to present a comprehensive review of current research activities that center on the shape-controlled synthesis of metal nanocrystals. We begin with a brief introduction to nucleation and growth within the context of metal nanocrystal synthesis, followed by a discussion of the possible shapes that a metal nanocrystal might take under different conditions. We then focus on a variety of experimental parameters that have been explored to manipulate the nucleation and growth of metal nanocrystals in solution-phase syntheses in an effort to generate specific shapes. We then elaborate on these approaches by selecting examples in which there is already reasonable understanding for the observed shape control or at least the protocols have proven to be reproducible and controllable. Finally, we highlight a number of applications that have been enabled and/or enhanced by the shape-controlled synthesis of metal nanocrystals. We conclude this article with personal perspectives on the directions toward which future research in this field might take.

Shape‐Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics?

Coated magnetite nanoparticles with a 6−8 nm average diameter were prepared. The surfactants used to stabilize the nanoparticles and disperse them in organic solvents were oleic acid (OA), lauric acid , dodecyl phosphonate, hexadecyl phosphonate, and dihexadecyl phosphate. Transmission electron microscopy analyses of the aggregation of the coated particles suggest that carboxylate surfactants provide the particles with better isolation and dispersibility as compared with phosphonate surfactants. However, Fourier transform infrared spectra of the phosphonate and phosphate coated particles suggest that these surfactants cover the surface of the nanoparticles in islands of high packing density. The thermogravimetric and differential scanning calorimetry measurements suggest that there is a quasi-bilayer of these surfactants covering the surface of the nanoparticles, with varying amounts of surfactant in the outer layer and with the second layer weakly bound to the primary layer through hydrophobic interactio...

Alkyl Phosphonate/Phosphate Coating on Magnetite Nanoparticles: A Comparison with Fatty Acids

Ordered Two‐Dimensional Arrays of Ferrite Nanoparticles

Three things largely determine the electronic properties of a crystal:  the energy levels of the atoms or lattice sites, the coupling between adjacent sites, and the symmetry of the solid. Imagine being able to control each of these properties separately, and therefore being able to “design” a solid with a prescribed set of electronic properties. For an atomic solid, this would amount to being able to tune the electronegativity of an atom, to control the strength of the covalent interactions within the lattice, and to choose the crystal structure. While the chemistry of the periodic table does not permit such control, the chemistry of “artificial atoms”,1 or quantum dots (QDs), does. In this Account, we will discuss one example of “designing” a unique electronic property into a QD solid. This property, which is the ability of the solid to reversibly pass through a metal−insulator (MI) transition under ambient conditions, is something that has not been previously demonstrated for a more traditional solid. A two-dimensional (2D) hexagonal superlattice of organically passivated silver QDs was fabricated as a Langmuir monolayer. Selecting a particular size of QD controlled the (super)lattice site energies. The coupling between adjacent QDs was coarsely controlled by selection of the organic surface passivant, and precisely controlled by compressing the superlattice using the Langmuir technique. By using the title “Architectonic2 Quantum Dot Solids”, we emphasize that many of the collective properties of the superlattice were rationally designed into the material.

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Architectonic Quantum Dot Solids

This paper reviews the recent advances in experiment and theory of the induction of chiroptical effects, primarily circular dichroism (CD), at the plasmonic and excitonic resonances of achiral inorganic nanocrystals (NCs) capped and/or formed with chiral molecules. It also addresses stronger chiroptical effects obtained in intrinsically chiral inorganic nanostructures obtained from growing enantiomeric excess of intrinsically chiral NCs or arranging achiral plasmonic particles in chiral configurations. The accumulated experimental data and theory on various CD induction mechanisms provide an extended set of tools to properly analyze and understand the electromagnetic influence of chiral molecules on inorganic particles and obtain new general insights into the interaction of capping molecules with inorganic NCs. Among the field-induced CD mechanisms developed recently one can name the Coulomb (near-field, dipolar) mechanism for nanostructures much smaller than the wavelength, and for larger nanostructures, the electromagnetic (effective chiral medium), and intrinsically chiral plasmonic mechanisms.

Chirality and chiroptical effects in inorganic nanocrystal systems with plasmon and exciton resonances

Silver nanocrystals grown on a poly(dG)-poly(dC) double stranded DNA scaffold displayed circular dichroism at their surface plasmon excitation band. This chiral plasmon signature was not observed in a control experiment where silver nanocrystals of similar size were produced without the DNA template and adsorbed to the DNA. It is concluded that the DNA templated Ag nanocrystals had a preferred structural handedness.

Gil Markovich

Papers

Alkyl Phosphonate/Phosphate Coating on Magnetite Nanoparticles: A Comparison with Fatty Acids

Ordered Two‐Dimensional Arrays of Ferrite Nanoparticles

Architectonic Quantum Dot Solids

Chirality and chiroptical effects in inorganic nanocrystal systems with plasmon and exciton resonances

Chirality of Silver Nanoparticles Synthesized on DNA