We describe and demonstrate a general strategy for engineering binary and ternary hybrid nanoparticles based on spontaneous epitaxial nucleation and growth of a second and third component onto seed nanoparticles in high-temperature organic solutions. Multifunctional hybrid nanoparticles that combine magnetic, plasmonic, and semiconducting properties and that are tunable in size and morphology can be realized, as demonstrated for combinations of Au, Fe3O4 and PbS or PbSe. The properties of each component within the hybrids can be modulated strongly by the conjugating component(s) aided by the coherent interfaces between them.

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 interactions between the alkyl chains. The desorption temperatures of the alkyl phosphonates and phosphate are higher than those of the carboxylate coated particles. The enthalpy of binding of the ligands suggests strong P−O−Fe bonding on the surface. Nevertheless, regardless of binding strength, the OA coated particles are better dispersed in organic solvents. Their higher hydrophobicity is likely due to different interactions among the oleyl chains and/or a smaller tendency to form bilayer structures.

A method is presented for the preparation of a biocompatible ferrofluid containing dye-functionalized magnetite nanoparticles that can serve as fluorescent markers. This method entails the surface functionalization of magnetite nanoparticles using citric acid to produce a stable aqueous dispersion and the subsequent binding of fluorescent dyes to the surface of the particles. Several ferrofluid samples were prepared and characterized using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), BET surface area analysis, transmission electron microscopy (TEM), and SQUID magnetometry. In addition, confocal fluorescence microscopy was used to study the response of the fluorescent nanoparticles to an applied magnetic field and their uptake by cells in vitro. Results are presented on the distribution of particle sizes, the fluorescent and magnetic properties of the nanoparticles, and the nature of their surface bonds. Biocompatible ferrofluids with fluorescent nanoparticles enable optical tracking of basic processes at the cellular level combined with magnetophoretic manipulation and should be of substantial value to researchers engaged in both fundamental and applied biomedical research.

A method is presented for synthesizing core-shell structures consisting of monodisperse polystyrene latex nanospheres as cores and gold nanoparticles as shells. Use of polystyrene spheres as the core in these structures is advantageous because they are readily available commercially in a wide range of sizes, and with dyes or other molecules doped into them. Gold nanoparticles, ranging in size from 1 to 20 nm, are prepared by reduction of a gold precursor with sodium citrate or tetrakis(hydroxymethyl)phosphonium chloride (THPC). Carboxylate-terminated polystyrene spheres are functionalized with 2-aminoethanethiol hydrochloride (AET), which forms a peptide bond with carboxylic acid groups on their surface, resulting in a thiol-terminated surface. Gold nanoparticles then bind to the thiol groups to provide up to about 50% coverage of the surface. These nanoparticles serve as seeds for growth of a continuous gold shell by reduction of additional gold precursor. The shell thickness and roughness can be controlled by the size of the nanoparticle seeds as well as by the process of their growth into a continuous shell. By variation of the relative sizes of the latex core and the thickness of the gold overlayer, the plasmon resonance of the nanoshell can be tuned to specific wavelengths across the visible and infrared range of the electromagnetic spectrum, for applications ranging from the construction of photonic crystals to biophotonics. The position and width of the plasmon resonance extinction peak are well-predicted by extended Mie scattering theory.

This paper presents the use of nanoscale chemistry to synthesize a multilevel, hierarchically built nanoparticle, which we define as a nanoclinic, for targeted diagnostics and therapy. This nanoclinic, produced by multistep chemistry in a nanosize micelle, consists of a thin silica shell encapsulating magnetic (Fe2O3) nanoparticles and fluorescent dyes for enhanced contrast magnetic resonance and optical imaging and magnetic-induced cancer therapy. Furthermore, the surface of these prototype nanoclinics is functionalized with a biotargeting group, luteinizing hormone-releasing hormone (LH−RH). In the work reported here, the LH−RH targets receptor-specific cancer cells for utilization in imaging and investigation of biological effects. The structure and function of these nanoclinics have been characterized using electron and X-ray diffractions, transmission electron microscopy, atomic force and scanning electron microscopy and two-photon laser scanning microscopy. Targeting of the receptor-specific cells has been demonstrated, along with the demonstration of a new mechanism of selective destruction of cancer cells, in a dc magnetic field, using these magnetic nanoclinics.

Fe3O4 nanoparticles in the size range of 8−12 nm have been prepared and allowed to self-assemble on GaAs substrates in the presence of strong magnetic fields. A long range ordering is observed in which the particles self-assemble into a distribution of elongated clusters with a predominant orientation lengthwise along the field direction. Hysteresis loops measured parallel and perpendicular to the alignment direction show substantial directional dependence. The coercive fields in the direction parallel to the alignment field are larger than those perpendicular to it by 57% and 136% at 100 and 5K, respectively. A broad peak is observed in magnetization profiles obtained with zero- field-cooling.

We report here straightforward solution-phase methods of preparing CdS NCs with a wide variety of morphologies, starting with oleylamine as the surfactant or capping agent, and varying the reaction conditions. We have systematically investigated the effects of temperature, precursor concentration, growth time, addition of metal nanoparticles, addition of cosurfactants, and acidification of the reaction medium on the growth of CdS NCs. These parameters have a tremendous impact on the morphology of the nanocrystals, allowing the controlled synthesis of a series of shapes including nanorods, bipods, tripods, tetrapods, nanocubes, nanowires, chain-like nanostructures, and nanoplatelets. At 100 °C, in the absence of secondary additives, we observed the nucleation of zinc blend CdS cores, followed by the growth of wurtzite arms to produce rods, bipods, and tripods. The addition of tetradecylphosphonic acid suppressed the growth of the wurtzite arms, resulting in zinc blend cubic nanocrystals. The addition of gold nanoparticles or acidification of the reaction medium led to nucleation and anisotropic growth of the wurtzite polymorph.

III−V semiconductor quantum dots are of considerable interest as their applications cover a broad spectrum, from optoelectronic to biomedical technology. For them to be of practical value, there is a need for a method that provides rapid and scalable production of highly monodispersed nanoparticles. This paper reports an efficient and rapid method of producing highly monodispersed InP quantum dots using a novel precursor-based colloidal synthesis in a noncoordinating solvent. The method also allows judicious control over the size of the quantum dots and can also be extended to produce other III−V quantum dots. In this paper, the synthesis and characterization of highly monodispersed InP quantum dots from newly prepared indium(III) carboxylate complexes in octadecene are detailed. When using indium(III) carboxylate as the indium precursor, no surfactant or coordinating solvents are required to prepare high-quality InP quantum dots in octadecene. The in situ formation of a surfactant upon injection of the phosphine precursor [P(SiMe3)3] helps control the growth of the resulting quantum dots. Structural and optical studies (continuous wave and time-resolved) have been performed on the as-prepared InP quantum dots. In addition, time-resolved photoluminescence has been conducted on etched InP quantum dots. The effects of the carboxylate chain length in indium(III) carboxylate and injection temperature on the growth and properties of quantum dots have been studied.