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Ordered arrays of palladium nanostructures have been obtained inside MCM-48 and SBA-15, using chemical vapor infiltration. Removal of the silica matrix affords porous three-dimensional Pd nanoballs and one-dimensional Pd nanowires, depending on the architecture of the silicate host.

Synthetic magnetic nanoparticles (MNPs) are emerging as versatile probes in biomedical applications, especially in the area of magnetic resonance imaging (MRI). Their size, which is comparable to biological functional units, and their unique magnetic properties allow their utilization as molecular imaging probes. Herein, we present an overview of recent breakthroughs in the development of new synthetic MNP probes with which the sensitive and target-specific observation of biological events at the molecular and cellular levels is possible.

Magnetic nanoparticles, which exhibit a variety of unique magnetic phenomena that are drastically different from those of their bulk counterparts, are garnering significant interest since these properties can be advantageous for utilization in a variety of applications ranging from storage media for magnetic memory devices to probes and vectors in the biomedical sciences. In this Account, we discuss the nanoscaling laws of magnetic nanoparticles including metals, metal ferrites, and metal alloys, while focusing on their size, shape, and composition effects. Their fundamental magnetic properties such as blocking temperature (Tb), spin life time (τ), coercivity (Hc), and susceptibility (χ) are strongly influenced by the nanoscaling laws, and as a result, these scaling relationships can be leveraged to control magnetism from the ferromagnetic to the superparamagnetic regimes. At the same time, they can be used in order to tune magnetic values including Hc, χ, and remanence (Mr). For example, life time of mag...

Magnetic nanoparticles exhibit unique nanoscale properties of superparamagnetism and have the potential to be utilized as excellent probes for magnetic resonance imaging (MRI). Especially, clinically benign iron oxide nanoparticles provide good MR probing capability and some of them are currently available for clinical applications. However, limited magnetic property and inability to escape from reticuloendothelial system (RES) of the currently used nanoparticles impede their further advancements and therefore it is necessary to develop advanced magnetic nanoparticle probes for next-generation molecular MR imaging. In this chapter, we overview recent progresses on the development of magnetic nanoparticle probes for molecular MR imaging. Utilization of these nanoparticle probes for both in vitro and in vivo molecular MR imaging will be described.

The sections in this article are Introduction Magnetic Nanoparticle Contrast Agents Silica- or Dextran-coated Iron Oxide Contrast Agents Magnetoferritin Magnetodendrimers and Magnetoliposomes New Type of Contrast Agent: Non-hydrolytically Synthesized High Quality Iron Oxide Nanoparticles Iron Oxide Nanoparticles in Molecular MR Imaging Infarct and Inflammation Angiogenesis Apoptosis Gene Expression Cancer Imaging Summary and Outlook

Magnetic nanoparticles exhibit unique nanoscale properties and their utilization for various magnetic systems is of significant interest. Especially, heterostructured magnetic nanoparticles are emerging as next-generation materials due to their synergistically enhanced magnetism and potential multifunctionalities. Herein, we overview the recent advances in the development of magnetic nanoparticles with a focus on multicomponent heterostructured nanoparticles including alloys, core-shells, and binary superlattices synthesized via nonhydrolytic methods. Their multifunctionalites and high performance capabilities are demonstrated for applications in high density magnetic storages, chemical catalysis, and biomedical separation and diagnostics.

Magnetic nanoparticles exhibit unique nanoscale properties of superparamagnetism and have the potential to be utilized as excellent probes for magnetic resonance imaging (MRI). Especially, clinically benign iron oxide nanoparticles provide good MR probing capability and some of them are currently available for clinical applications. However, limited magnetic property and inability to escape from reticuloendothelial system (RES) of the currently used nanoparticles impede their further advancements and therefore it is necessary to develop advanced magnetic nanoparticle probes for next-generation molecular MR imaging. In this chapter, we overview recent progresses on the development of magnetic nanoparticle probes for molecular MR imaging. Utilization of these nanoparticle probes for both in vitro and in vivo molecular MR imaging will be described.

Hybrid nanoparticles are of significant interest primarily because of their innate multifunctional capabilities. These capabilities can be exploited when hybrid nanoparticles are used for applications in the biomedical sciences in particular, where they are utilized as multimodal nanoplatforms for sensing, imaging, and therapy of biological targets. However, the realization of their biomedical applications has been difficult, in part because of a lack of high quality hybrid nanoparticles which possess high aqueous colloidal stability and biocompatibility while retaining their multifunctionalities. Here, we present the development of inorganic heterodimer nanoparticles of FePt-Au with multifunctional capabilities including catalytic growth effects, magnetic resonance (MR) contrast effects, optical signal enhancing properties, and high colloidal stability and biocompatibility. Their multimodal capabilities for biological detection are demonstrated through their utilizations in the patterned biochip based detection of avidin-biotin interaction as well as in molecular MR imaging of neuroblastoma cells.

Shape controlled synthesis of inorganic nanocrystals is one of the important issues in materials chemistry due to their novel shape dependent properties. Although various shapes of nanocrystals have been developed, a systematic account on the shape control of these nanocrystals still remains an important subject in materials chemistry. In this article, we will overview the recent developments in the geometrical shape evolution of semiconductor and metal oxide nanocrystals obtained by nonhydrolytic synthetic methods. Many structurally unprecedented motifs have appeared as zero-dimesional (D) polyhedrons, one-D rods and wires, two-D plates and prisms, and other advanced shapes such as branched rods, stars, and inorganic dendrites. Important parameters which determine the geometrical shapes of nanocrystals are also illustrated. In addition, as a possible application of such nanocrystals for biomedical sciences, we further describe their utilizations for cancer diagnosis through nanocrystal-assisted magnetic resonance imaging (MRI).

Inorganic nanocrystals with tailored geometries exhibit unique shape-dependent phenomena and subsequent utilization of them as building blocks for the fabrication of nanodevices is of significant interest. Herein, we review the recent developments in the shape control of colloidal nanocrystals with a focus on the scientifically and technologically important semiconductor and metal oxide nanocrystals obtained by nonhydrolytic synthetic methods. Many structurally unprecedented motifs have been discovered including polyhedrons, rods and wires, plates and prisms, and other advanced shapes such as branched rods, stars, inorganic dendrites, and dumbbells. The currently proposed shape-guiding mechanisms are presented and the important pioneering studies on the assembly of shape-controlled nanocrystals into ordered superlattices and the fabrication of prototype advanced nanodevices are discussed.

A comprehensive study of iron oxide nanocrystal growth through non-hydrolitic, surfactant-mediated thermal reaction of iron pentacarbonyl and an oxidizer has been conducted, which includes size control, anisotropic shape evolution, and crystallographic phase transition of monodisperse iron oxide colloidal nanocrystals. The reaction was monitored via in situ UV-vis spectroscopy, taking advantage of the color change accompanying the iron oxide colloid formation, allowing measurement of the induction time for nucleation. Features of the synthesis such as the size control and reproducibility are related to the occurrence of the observed delayed nucleation process. As a separate source of iron and oxygen is adopted, phase control could also be achieved by sequential injections of oxidizer.

High-quality biocompatible magnetic iron oxide (Fe3O4) nanocrystals were developed through a ligand exchange process of hydrophobically capped nanocrystals with hydrophilic molecules. By simple modulation of the nanocrystal surface ligand charge properties, we have been able to prepare magnetic nanocrystals with excellent intracellular labeling capabilities that efficiently label a variety of cell types without the need for additional transport facilitating agents. The excellent intracellular labeling capability of the newly developed cationic WSIO has further led to successful MRI monitoring of the migration of neural stem cells in rat spinal cord. The magnetic nanocrystals developed here have great potential in applications for labeling of various cell types and also the monitoring of cell-based medical treatments and cancer metastasis.

Spontaneous one dimensional arrangements of spherical Au nanoparticles were accomplished by using a liquid crystalline thiol ligand, 4′-(12-mercaptododecyloxy)biphenyl-4-carbonitrile. Simple thermal treatment of Au nanoparticles with the ligands showed 1D ordering of the Au nanoparticles.

Crystals consist of a periodic alternation of specific repeating molecules. The individual repeating molecules have quantized electronic structures while crystals have continuous electronic band structures that result from the overlap and combination of molecular orbitals of repeating molecules. Therefore, isolated molecules exhibit quantum mechanical properties, while the chemical and physical properties of bulk crystals obey the laws of classical mechanics. However, when the crystal size decreases into the nano-scale regime (1 ∼ 100 nm), the electronic band of the crystals starts to be quantized and the resulting nanocrystals behave as an intermediate between molecules and crystals.2, 3, 4, 5 These nanocrystals exhibit novel properties which differ from both molecular and bulk properties. For example, CdSe semiconductor crystals on the 10 nm scale, the characteristic red luminescence is no longer observed but the luminescence can be continuously tuned from red to blue by varying the crystal size. The melting temperature of nanocrystals simultaneously decreases when the nanocrystal size is reduced.6,7 In the nanoscopic world, crystal properties are highly dependent on the size, shape, and surface state of the crystals.

We demonstrate a novel synthetic scheme that can be used to control the crystalline phase and shape of GaP semiconductor nanocrystals. Our study shows that steric effects of surfactant ligands can modulate the crystalline phases and control the shapes of nanocrystals. The shape of the nanocrystals obtained varies from zero-dimensional spheres to one-dimensional rods via controlling the ratio between primary and tertiary alkylamines. III-V semiconductors (in our case: GaP) under 10 nm in width are first reported, and unique optical properties due to shape anisotropy are also observed.

A simple one-pot synthesis of size and shape controlled ZnTe nanocrystals using a monomeric molecular precursor, [Zn(TePh)2][TMEDA], has been studied by varying the growth temperature or the templating surfactants.

Ordered arrays of palladium nanostructures have been obtained inside MCM-48 and SBA-15, using chemical vapor infiltration. Removal of the silica matrix affords porous three-dimensional Pd nanoballs and one-dimensional Pd nanowires, depending on the architecture of the silicate host.

Our study describes a convenient one-step synthesis of ZnSe and ZnTe nanocrystals (NC) whose sizes and shapes are precisely tuned by varing the growth temperature or stabilizing surfactants. We utilized molecular precursors, bis(phenylselenolate or phenyltellurolato)zinc -N,N,N',N'-tetramethylethylenediamine (TMEDA), which effectively produce 0-dimensional sphere or 1-dimensional nanorods of ZnSe or ZnTe, respectively. Nanocrystals are highly monodispersed and luminescent; the emission wavelength varies over a wide range depending on the particle size. This study constitutes a nice demonstration of direct size and shape controlled synthesis of semiconductor nanocrystals and this method can be extended to the synthesis of nanocrystals of other materials.

Since the use of magnetic nanocrystals as probes for biomedical system is attractive, it is important to develop optimal synthetic protocols for high-quality magnetic nanocrystals and to have the systematic understanding of their nanoscale properties. Here we present the development of a synthetically controlled magnetic nanocrystal model system that correlates the nanoscale tunabilities in terms of size, magnetism, and induced nuclear spin relaxation processes. This system further led to the development of high-performance nanocrystal-antibody probe systems for the diagnosis of breast cancer cells via magnetic resonance imaging.

Thiacrownether-mediated self-assembly of Au nanoparticles produced a larger sized aggregation of which grain size was controlled by the relative concentration and the structure of thiacrownethers. ...

We demonstrate a novel synthetic scheme that can be used to differentially guide the shape of PbS semiconductor nanocrystals. Our study first demonstrates the discovery of single-crystalline star-shaped nanocrystals as novel transient species. We then carefully probe their shape evolution toward other novel nanostructures (e.g., tadpole-, L-, T-, cross-shapes, highly faceted star shapes, truncated octahedrons and cubes, etc.) and systematically elucidate the key parameters that control these final structures. In principle, through programming these growth parameters, the desired architecture of building blocks of other kinds of nano materials can be constructed.

A novel twinning-driven hyper-branching mechanism of 1-dimensional nanowires is demonstrated to provide a clear understanding of the growth behaviour of a complex nanocrystal structure. Specifically, we have discovered that the multiple twinning mechanism can be successfully applied to the hyper-branching of nanowires. Systematic variations of TiO2 hyper-branching in terms of branching multiplicity, branching angle, and size were observed, depending on the sequence, the degree, and the combination of two different twinning modes of contact and interpenetration. The twinning process is a reliable synthetic protocol for next generation nanostructures which require highly complex, but predictable shape and symmetry.

A simple one-pot synthesis of size and shape controlled ZnTe nanocrystals using a monomeric molecular precursor, [Zn(TePh)2][TMEDA], has been studied by varying the growth temperature or the templating surfactants.

One-step size-controlled synthesis of ZnSe quantum dots is studied and the obtained QDs are luminescent with the emission wavelength varying over a wide range (up to 100 nm) depending on the particle size; the single-molecular precursor is an air-stable bis(phenylselenolato)zinc N,N,N′,N′-tetramethylethylenediamine (TMEDA) complex, which effectively affords different sizes of ZnSe QDs depending on growth temperatures.

A magnetic field is successfully utilized to induce the fabrication of size controllable one-dimensional (1-D) supercrystals which are composed of a highly crystalline assembly of fcc-packed cobalt nanoparticles; the anisotropy associated supercrystal magnetism is enhanced with four times higher coercivity than that of randomly aggregated nanoparticles.

Remarkable selectivity is achieved in the cleavage of benzyl ethers using ball-shaped palladium nanocatalysts, Pd@MCM-48, in an MCM-48 matrix. The unique nanocatalysts not only feature unprecedented complete hydrogenolysis selectivity of a benzyl ether over hydrogenation of a double bond, but also demonstrate selective cleavage of unsubstituted benzyl ether over substituted benzyl ethers.