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Notch signaling is a key cell-to-cell communication mechanism during development and in normal tissue maintenance and cancer. Signals exchanged between neighboring cells via Notch can reinforce molecular differences which eventually direct the fate decision of individual cells. Despite increasing knowledge of these signaling events, little is known about how spatiotemporal dynamics of the receptor signaling across a cell influence the signal exchange. In this presentation, we introduce an advanced nano-probing system that mimics binary cell communication via Notch, while providing systematic spatiotemporal control of Notch signaling in live cells. This new nanosystem enabled simultaneous observation of Notch dynamics and signal activation with single molecule resolution in live cells for the first time. We envision this nano-probing system as a next generation force microscopy technology platform to quantify and control force-mediated biological processes at the subcellular level.

The deposition of MoS2 and TiS2 thin films from the metal-organic precursors Mo(S-t-Bu)4 and Ti(S-t-Bu)4 has been investigated. Stoichiometric films with low levels of oxygen and carbon contaminants can be grown at temperatures between 110 and 350 °C and low pressure. The films are amorphous when grown at these low temperatures and have granular morphologies in which the grains are 30−90 nm in diameter, the larger grain sizes being observed at higher deposition temperatures. For the MoS2 deposits, the electrical conductivity was ∼1 Ω-1cm-1. For both precursors, the organic byproducts generated during deposition consist principally of isobutylene and tert-butylthiol; smaller amounts of hydrogen sulfide, isobutane, di-tert-butyl sulfide, and di-tert-butyl disulfide are also generated. A β-hydrogen abstraction/proton-transfer mechanism accounts for the distributions of the organic byproducts seen during the deposition of MoS2 and TiS2 films. Our results differ in some respects from those of a previous study ...

The chemical pathway responsible for the conversion of the organotitanium compound tetraneopentyltitanium to titanium carbide has been studied under chemical vapor conditions and on single crystals in ultra-high vacuum. For every equivalent of TiNp4 consumed in the deposition process, 3.28 equiv of neopentane and 0.16 equiv of isobutane are produced; other organic species are also formed but in relatively small amounts. About 93% of the carbon and hydrogen originally present in the precursor can be accounted for in these products. Thermolysis of the specifically deuterated analogue Ti(CD2CMe3)4 yields a 2.25:1 ratio of neopentane-d3 and neopentane-d2; this result combined with a kinetic isotope effect of 4.9 at 385 K shows unequivocally that the first step in the deposition pathway under CVD conditions is α-hydrogen abstraction. The α-hydrogen abstraction step produces 1 equiv of neopentane and a titanium alkylidene, which undergoes further α- (and eventually γ-) hydrogen activation processes to generate ...

Studies of the thermolysis of Ti(CH2CMe3)4 in solution have been carried out in parallel with studies of the chemical mechanism responsible for its conversion to titanium carbide under CVD conditions. In hydrocarbon solutions, the neopentyl complex thermolyzes to eliminate 2.1 equiv of neopentane as the principal organic product. A deuterium kinetic isotope effect (kR(H)/kR(D) ) 5.2 ( 0.4) upon deuterating the alkyl groups at the R positions provides clear evidence that the initial step in the thermolysis is an R-hydrogen abstraction reaction to form neopentane. The activation parameters for this R-hydrogen abstraction process are ¢H q ) 21.5 ( 1.4 kcal/mol and ¢S q )- 16.6 ( 3.8 cal/(mol K). The titanium-containing product of this reaction is a titanium alkylidene, which in solution activates C-H bonds of both saturated and unsaturated hydrocarbon solvents such as benzene and cyclohexane. No activation of the C-F bonds of hexafluorobenzene is seen, however. Under special circumstances, a second thermolysis pathway for TiNp4 can be detected, A-hydrogen activation, but this pathway is intrinsically about 25 times slower than the R-hydrogen abstraction process.

NiS and PdS thin films are prepared at 10-2 Torr from the single-source precursors M(S2COCHMe2)2, M = Ni and Pd. Two different vapor deposition processes, photochemical and thermal, are employed. Gas-phase emission spectroscopy is used during the photochemical deposition to identify the two elemental components of the final materials, the metal atom and sulfur, in the gas phase. NiS and PdS thin films are grown by the thermal process at 300 and 350 °C, respectively, on Si and quartz substrates. The NiS films are highly oriented rhombohedral (γ) phase, and the PdS films are tetragonal-phase polycrystalline. The metal sulfide films are grown photolytically by 308 nm laser irradiation of the gas-phase precursors at lower temperatures (near the sublimation temperature). The NiS films show no X-ray diffraction patterns, but the PdS films are polycrystalline tetragonal phase. The films are analyzed by various surface analytical tools including scanning electron microscopy, X-ray photoelectron, and Rutherford ba...

ZnS thin films are made by laser driven chemical vapor deposition (CVD) from a single-source precursor, Zn(S{sub 2}COCHMe{sub 2}){sub 2} under vacuum conditions. Photofragments in the gas phase are identified simultaneously by luminescence spectroscopy. The laser selectively activates the initial decomposition of the precursor and drives its conversion to the desired materials under mild conditions. These photolytically produced films are compared to films made by thermal deposition from the same precursor. The deposits from both techniques, characterized by X-ray diffraction, Rutherford backscattering, and X-ray photoelectron spectroscopy, are pure stoichiometric ZnS in the hexagonal phase. Surface morphology differs in shape and granule size. During the laser-driven CVD process, gas-phase photochemical intermediates are identified by luminescence spectroscopy. The luminescent photoproducts are Zn and S{sub 2}, the two elemental components of the final material. Photofragmentation mechanisms leading to ZnS, the luminescent species Zn and S{sub 2}, and the gaseous organic byproducts are discussed. Further characterization of photofragmentation pathways is provided by the trapping of the photoreaction products and by mass spectroscopy. 34 refs., 6 figs.

Texaphyrins are pentaaza expanded porphyrins with the ability to form stable complexes with a variety of metal cations, particularly those of the lanthanide series. In biological milieus, texaphyrins act as redox mediators and mediate the production of reactive oxygen species (ROS). In this review, newer studies involving texaphyrin complexes targeting several different applications in anticancer therapy are described. In particular, the preparation of bismuth and lead texaphyrin complexes as potential α-core emitters for radiotherapy is detailed, as are gadolinium texaphyrin functionalized magnetic nanoparticles with features that make them of interest as dual-mode magnetic resonance imaging contrast agents and as constructs with anticancer activity mediated through ROS-induced sensitization and concurrent hyperthermia. Also discussed are gadolinium texaphyrin complexes as possible carrier systems for the targeted delivery of platinum payloads.

This review presents recent advances in synthetic methods and structural transformations of colloidal 2D layered metal chalcogenide nanocrystals. Planar 2D anisotropy and interlayer van der Waals gaps are the important characteristics of these nanocrystals for pristine disc, plate or sheet morphologies. These 2D nanocrystals undergo unique chemical transformations upon exposure to external chemical stimuli and newly obtained structures are 2D nanostructures with high complexity in their morphological geometries and chemical compositions. Finally, future opportunities and potential applications of 2D layered metal chalcogenide nanocrystals are briefly discussed.

Thin films of In{sub 2}Se{sub 3} have been prepared by metal-organic chemical vapor deposition (MOCVD) using volatile In[SeC(SiMe{sub 3}){sub 3}]{sub 3} as the precursor. The influence of growth parameters on the formation of crystalline phases and on the morphologies of In{sub 2}Se{sub 3} films were examined by X-ray diffraction and scanning electron microscopy. The stoichiometry of the films was determined by Rutherford backscattering spectroscopy (RBS). 36 refs., 4 figs., 2 tabs.

This review presents recent advances in synthetic methods and structural transformations of colloidal 2D layered metal chalcogenide nanocrystals. Planar 2D anisotropy and interlayer van der Waals gaps are the important characteristics of these nanocrystals for pristine disc, plate or sheet morphologies. These 2D nanocrystals undergo unique chemical transformations upon exposure to external chemical stimuli and newly obtained structures are 2D nanostructures with high complexity in their morphological geometries and chemical compositions. Finally, future opportunities and potential applications of 2D layered metal chalcogenide nanocrystals are briefly discussed.

A precise control and understanding of the magnetization dynamics of nanostructures is an important topic in applied nanosciences. Herein, we perform such control by annealing crystalline (Co/core)-(Pt/shell) nanoparticles. Using electron tomography, temperature dependent electron microscopy and time-resolved magneto-optics, we establish a clear correlation between the magnetization dynamics and the crystalline structure of the nanoparticles. For a mild laser annealing (370 K) the Co-Pt nanoparticles keep their core-shell structure and remain superparamagnetic with a blocking temperature T(B) = 66 K. Their time-resolved reflectivity shows that they are locally organized into a supra-crystalline ordered layer in the region of the laser spot. In contrast, a thermal annealing at higher temperatures (up to 700 K) modifies the structure of the individual nanoparticles into a CoPt crystalline ferromagnetic phase, with T(B,anneal) = 347 K. Correspondingly, the magneto-crystalline anisotropy of the annealed CoPt nanoparticles increases and their magnetization dynamics displays a motion of precession, characteristic of ferromagnetic nanostructures and which is absent in the superparamagnetic Co-Pt core-shells.

The organometallic compounds bis(allyl)zinc and bis(2-methylallyl)zinc have been shown to serve as MOCVD precursors for the deposition of zinc at temperatures as low as 150{degrees}C. The deposits on Si(100) wafers, quartz, copper, and aluminum consist of aggregates of hexagonal plates and columns. On silicon(100) substrates and at low background pressures (10{sup {minus}4} Torr), the zinc crystals are oriented preferentially with their c axes perpendicular to the silicon surface. The organic byproducts generated under CVD conditions are 1,5-hexadiene (76 mol%), 2-methyl-1,4-pentadiene (14 mol%), and propene (10 mol%); except for the pentadiene product, analogous hydrocarbons in similar amounts are formed when bis(2-methylallyl)zinc is used as the precursor. In situ spectroscopic studies on single-crystal Cu(111) substrates show that bis(allyl)zinc transfers its allyl groups to the surface below 250{degrees}C; the surface-bound allyl groups are probably bound in a trihapto fashion. On clean surfaces, the allyl groups react between 10 and 130{degrees}C to give propene and smaller amounts of 2-methyl-1,4-pentadiene. The propene is the result of transfer of a hydrogen atom to the surface allyl groups; the source of the hydrogen atoms has been traced to the sacrificial fragmentation of some of the allyl groups. The dehydrogenation of some of the surface allyl groups also more » gives rise to hydrogen-deficient hydrocarbon fragments, which eventually convert to a carbonaceous overlayer. Once the overlayer is formed, fragmentation of allyl groups is inhibited and, instead, coupling of allyl groups to 1,5-hexadiene is the predominant reaction channel. Passage of a mixture of bis(2-methylallyl)zinc and bis(2-methylallyl)palladium over substrates at 250{degrees}C and 10{sup {minus}2} Torr results in the deposition of Zn/Pd alloys. 47 refs., 12 figs. « less

We demonstrate that the controlled distribution of nanoparticles can be achieved by employing the spin-coating method. The Co and Ag nanoparticles were uniformly distributed on the Si and SiO2 substrates with this method. The particle density was controllable by varying the concentration of colloids. The spatial distribution of the nanoparticles within the patterned area was also shown to be uniform with small boundary effect, which is favorable for current microelectronics technology. We propose that the spin-coating method can be utilized in developing mass production processes for future nanodevices.

This study provides an easy and simple method to obtain inorganic nanoparticles that can penetrate the blood–brain barrier, the heavily guarded system in the brain, via cross-linked serum albumin surface coatings. Their intact BBB permeability was confirmed in both in vitro and in vivo tests.

Early detection and treatment of disease is the most important component of a favorable prognosis. Biomedical researchers have thus invested tremendous effort in improving imaging techniques and treatment methods. Over the past decade, concepts and tools derived from nanotechnology have been applied to overcome the problems of conventional techniques for advanced diagnosis and therapy. In particular, advances in nanoparticle technology have created new paradigms for theranostics, which is defined as the combination of therapeutic and diagnostic agents within a single platform. In this Account, we examine the potential advantages and opportunities afforded by magnetic nanoparticles as platform materials for theranostics. We begin with a brief overview of relevant magnetic parameters, such as saturation magnetization, coercivity, and magnetocrystalline anisotropy. Understanding the interplay of these parameters is critical for optimizing magnetic characteristics needed for effective imaging and therapeutics, which include magnetic resonance imaging (MRI) relaxivity, heat emission, and attractive forces. We then discuss approaches to constructing an MRI nanoparticle contrast agent with high sensitivity. We further introduce a new design concept for a fault-free contrast agent, which is a T1 and T2 dual mode hybrid. Important capabilities of magnetic nanoparticles are the external controllability of magnetic heat generation and magnetic attractive forces for the transportation and movement of biological objects. We show that these functions can be utilized not only for therapeutic hyperthermia of cancer but also for controlled release of cancer drugs through the application of an external magnetic field. Additionally, the use of magnetic nanoparticles to drive mechanical forces is demonstrated to be useful for molecular-level cell signaling and for controlling the ultimate fate of the cell. Finally, we show that targeted imaging and therapy are made possible by attaching a variety of imaging and therapeutic components. These added components include therapeutic genes (small interfering RNA, or siRNA), cancer-specific ligands, and optical reporting dyes. The wide range of accessible features of magnetic nanoparticles underscores their potential as the most promising platform material available for theranostics.

We present a colloidal route for the synthesis of ultrathin ZrS(2) (UT-ZrS(2)) nanodiscs that are ~1.6 nm thick and consist of approximately two unit cells of S-Zr-S. The lateral size of the discs can be tuned to 20, 35, or 60 nm while their thickness is kept constant. Under the appropriate conditions, these individual discs can self-assemble into face-to-face-stacked structures containing multiple discs. Because the S-Zr-S layers within individual discs are held together by weak van der Waals interactions, each UT-ZrS(2) disc provides spaces that can serve as host sites for intercalation. When we tested UT-ZrS(2) discs as anodic materials for Li(+) intercalation, they showed excellent nanoscale size effects, enhancing the discharge capacity by 230% and greatly improving the stability in comparison with bulk ZrS(2). The nanoscale size effect was especially prominent for their performance in fast charging/discharging cycles, where an 88% average recovery of reversible capacity was observed for UT-ZrS(2) discs with a lateral diameter of 20 nm. The nanoscale thickness and lateral size of UT-ZrS(2) discs are critical for fast and reliable intercalation cycling because those dimensions both increase the surface area and provide open edges that enhance the diffusion kinetics for guest molecules.

The immune-response of macrophages is an important area of investigation since it represents the major pathway by which early-stage defense barriers are established in skin, lungs, and mucosal systems to counteract foreign objects. In this study, we have examined the size-dependent inflammatory and toxicological effects of nanostructured silver particles (nano-Ag) on macrophage immune cells.

When decoupled from the overlying membrane, hair bundles of the amphibian sacculus exhibit spontaneous oscillation. To explore the dynamics of this innate motility without an imposed external load, we recorded their oscillations with a high‐speed CMOS camera, and applied mechanical manipulation that minimally alters the geometry of an individual hair bundle. We present a technique that utilizes micron‐sized magnetic particles to actuate the stereociliary bundle with a magnetized probe. Quasi‐steady‐state displacements were imposed on freely oscillating bundles. Our data indicate that deflection of the bundle affects both the frequency and the amplitude of the oscillations, with a crossing of the bifurcation that is dependent on the direction and speed of the applied offset.

Achieving high accuracy in the imaging of biological targets is a challenging issue. For MRI, to enhance imaging accuracy, two different imaging modes with specific contrast agents are used; one is a T1 type for a “positive” MRI signal and the other is a T2 type for a “negative” signal. Conventional contrast agents respond only in a single imaging mode and frequently encounter ambiguities in the MR images. Here, we propose a “magnetically decoupled” core−shell design concept to develop a dual mode nanoparticle contrast agent (DMCA). This DMCA not only possesses superior MR contrast effects but also has the unique capability of displaying “AND” logic signals in both the T1 and T2 modes. The latter enables self-confirmation of images and leads to greater diagnostic accuracy. A variety of novel DMCAs are possible, and the use of DMCAs can potentially bring the accuracy of MR imaging of diseases to a higher level.

ZnS thin films are made by laser driven chemical vapor deposition (CVD) from a single-source precursor, Zn(S{sub 2}COCHMe{sub 2}){sub 2} under vacuum conditions. Photofragments in the gas phase are identified simultaneously by luminescence spectroscopy. The laser selectively activates the initial decomposition of the precursor and drives its conversion to the desired materials under mild conditions. These photolytically produced films are compared to films made by thermal deposition from the same precursor. The deposits from both techniques, characterized by X-ray diffraction, Rutherford backscattering, and X-ray photoelectron spectroscopy, are pure stoichiometric ZnS in the hexagonal phase. Surface morphology differs in shape and granule size. During the laser-driven CVD process, gas-phase photochemical intermediates are identified by luminescence spectroscopy. The luminescent photoproducts are Zn and S{sub 2}, the two elemental components of the final material. Photofragmentation mechanisms leading to ZnS, the luminescent species Zn and S{sub 2}, and the gaseous organic byproducts are discussed. Further characterization of photofragmentation pathways is provided by the trapping of the photoreaction products and by mass spectroscopy. 34 refs., 6 figs.

This paper reports the facile photochemical synthesis of binary and ternary II/VI metal sulfides from single-source diethyl dithiocarbamate zinc and cadmium precursors, M(S{sub 2}-CNEt{sub 2}){sub 2}, M = Zn, Cd. Photoluminescence spectroscopy is used to simultaneously identify gas phase species present during the CVD process. This study demonstrates one of the first uses of light for both deposition and real time characterization of gas phase species in multiphase materials synthesis. It is demonstrated that ternary Zn{sub x}Cd{sub 1-x}S films as well as ZnS and CdS can be prepared photochemically under mild conditions and only in the area irradiated by the laser beam. Luminescence spectra show that the elements composing the films are produced in the gas phase. 20 refs., 2 figs., 1 tab.

Photolysis of M(NEt2)4 in the gas phase produces diatomic MN molecules (M = Ti, Zr, Hf). TiN and ZrN molecules were identified in the gas phase under CVD conditions by emission spectroscopy and time-of-flight mass spectroscopy. Nanostructured deposits of TiN were formed on quartz substrates by irradiating Ti(NEt2)4 gas at 355 nm. These studies demonstrate the gas phase formation of diatomic molecules having the same stoichiometry as that of the desired solid-phase deposit.

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.

Current biomedical imaging techniques including magnetic resonance imaging (MRI), positron emission tomography (PET), and computed X-ray tomography (CT) are vital in the diagnosis of various diseases. Each imaging modality has its own merits and disadvantages, and a single technique does not possess all the required capabilities for comprehensive imaging. Therefore, multimodal imaging methods are quickly becoming important tools for state-of-the-art biomedical research and clinical diagnostics and therapeutics. In this Account, we will discuss synergistically integrated nanoparticle probes, which will be an essential tool in multimodal imaging technology. When inorganic nanoparticles are introduced into biological systems, their extremely small size and their exceptional physical and chemical properties make them useful probes for biological diagnostics. Nanoparticle probes can endow imaging techniques with enhanced signal sensitivity, better spatial resolution, and the ability to relay information about ...

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...

Co@Pt-Au nanoparticles, which have enhanced magnetism and high stability in aqueous media, are utilized in conjunction with MRI to monitor the structural evolution of Abeta assemblies, especially Abeta protofibrils in the early reversible stages.

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 inside cover displays multifunctional “adenovirus-magnet” nanoparticles possessing target-specific infection, magnetic resonance imaging (MRI), and gene expression capabilities. These hybrid nanoparticles, reported by Jin-Suck Suh, Jinwoo Cheon, and co-workers on p. 3109 in the Special Section on Bionanotechnology, selectively target the Coxsackievirus B adenovirus receptor (CAR)-positive cells and deliver the gene of enhanced green fluorescent protein (eGFP), while simultaneously being imaged by MRI. These hybrid nanoparticles can be regarded as new probes for in vivo MRI tracking of targeted viral gene delivery, which is essential for next-generation diagnostics and therapeutics.

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.

Co@Pt nanoparticles as a bifunctional nanoplatform system for the hydrogenation of various unsaturated organic molecules under mild conditions and also for magnetic separation and recycling are demonstrated.

Massive fabrication of free-standing Co/Pt magnetic barcode nanowires with well-defined interfaces and layer thicknesses is obtained after freeing them from porous templates. Such barcodes display bamboo-like shapes with identical motifs either inside or out of the templates. The ferromagnetism of these barcode nanowires can be modulated easily depending on the cobalt segments and shape anisotropies. Further enhancements of the ferromagnetism of Co/Pt barcodes are also accomplished through interfacial alloying processes via a thermally induced phase transition.

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.

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.