/pdf/self-assembled-monolayers-of-thiolates-on-metals-as-a-form-1neb0hj3k4.pdf

Self-assembled monolayers of thiolates on metals as a form of nanotechnology.

Research on fluorescent semiconductor nanocrystals (also known as quantum dots or qdots) has evolved over the past two decades from electronic materials science to biological applications. We review current approaches to the synthesis, solubilization, and functionalization of qdots and their applications to cell and animal biology. Recent examples of their experimental use include the observation of diffusion of individual glycine receptors in living neurons and the identification of lymph nodes in live animals by near-infrared emission during surgery. The new generations of qdots have farreaching potential for the study of intracellular processes at the single-molecule level, high-resolution cellular imaging, long-term in vivo observation of cell trafficking, tumor targeting, and diagnostics.

/pdf/quantum-dots-for-live-cells-in-vivo-imaging-and-diagnostics-3y9ayecoh8.pdf

Quantum Dots for Live Cells, in Vivo Imaging, and Diagnostics

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.

We report a synthesis of highly luminescent (CdSe)ZnS composite quantum dots with CdSe cores ranging in diameter from 23 to 55 A. The narrow photoluminescence (fwhm ≤ 40 nm) from these composite dots spans most of the visible spectrum from blue through red with quantum yields of 30−50% at room temperature. We characterize these materials using a range of optical and structural techniques. Optical absorption and photoluminescence spectroscopies probe the effect of ZnS passivation on the electronic structure of the dots. We use a combination of wavelength dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, small and wide angle X-ray scattering, and transmission electron microscopy to analyze the composite dots and determine their chemical composition, average size, size distribution, shape, and internal structure. Using a simple effective mass theory, we model the energy shift for the first excited state for (CdSe)ZnS and (CdSe)CdS dots with varying shell thickness. Finally, we characterize the...

(CdSe)ZnS Core-Shell Quantum Dots - Synthesis and Characterization of a Size Series of Highly Luminescent Nanocrystallites

▪ Abstract Solution phase syntheses and size-selective separation methods to prepare semiconductor and metal nanocrystals, tunable in size from ∼1 to 20 nm and monodisperse to ≤5%, are presented. Preparation of monodisperse samples enables systematic characterization of the structural, electronic, and optical properties of materials as they evolve from molecular to bulk in the nanometer size range. Sample uniformity makes it possible to manipulate nanocrystals into close-packed, glassy, and ordered nanocrystal assemblies (superlattices, colloidal crystals, supercrystals). Rigorous structural characterization is critical to understanding the electronic and optical properties of both nanocrystals and their assemblies. At inter-particle separations 5–100 A, dipole-dipole interactions lead to energy transfer between neighboring nanocrystals, and electronic tunneling between proximal nanocrystals gives rise to dark and photoconductivity. At separations <5 A, exchange interactions cause otherwise insulating ass...

Synthesis and Characterization of Monodisperse Nanocrystals and Close-Packed Nanocrystal Assemblies

THE recent syntheses1,2 of macroscopic quantities of C60 have suggested possible applications in host–guest and organic chemistry, tribology, electrochemistry and semiconductor tech-nology. Here we report the preparation of alkali-metal-doped films of C60 and C70 which have electrical conductivities at room temperature that are comparable to those attained by n-type doped polyacetylene. The highest conductivities observed in the doped films are: 4Scm−1 (Cs/C60), 100 (Rb/C60), 500 (K/C60), 20 (Na/C60), 10 (Li/C60), 2 (K/C70). The doping process is reversed on exposure of the films to the atmosphere. At high doping levels, the films become more resistive. We attribute the conductivity induced in these films to the formation of energy bands from the π orbitals of C60 or C70, which become partially filled with carriers on doping. The smaller alkali metal ions should be able to fit into the interstices in the lattice without disrupting the network of contacts between the carbon spheroids. In the case of C60, this would allow the development of an isotropic band structure, and we therefore propose that these materials may constitute the first three-dimensional 'organic' conductors.

Conducting films of C60 and C70 by alkali-metal doping

Composite semiconductor crystallites involving CdSe grown on an ZnS seed, and vice versa, have been synthesized and capped with organic ligands in inverse micelle solutions. These composite particles, as well as capped seed crystallites of CdSe and ZnS, are isolated, purified, and characterized for relative atomic composition, structure, and electronic properties. The Debye X-ray scattering equation, when solved for these layered particles, shows that powder X-ray scattering is insensitive to a small foreign inclusion. A simple theoretical model for the LUMO and HOMO of layered crystallites shows that a small (< 15-{angstrom} diameter) interior foreign seed causes only small shifts of the lowest excited state, to either higher or lower energies. The capped CdSe seed and the capped CdSe portion of the layered particle grown on a ZnSe seed undergo low-temperature (169{degree}C) annealing to give near-single-crystal X-ray scattering. However, CdSe annealing is blocked by a surface ZnS layer which is ca. 4 {angstrom} thick. While growth to make composite particles does occur, neither particle shows evidence for epitaxial growth.

Nucleation and Growth of CdSe on ZnS Quantum Crystallite Seeds and Vice Versa, in Inverse Micelle Media

NANOMETRE-SCALE semiconductor quantum crystallites exhibit size-dependent and discrete excited electronic states which occur at energies higher than the band gap of the corresponding bulk solid1–4. These crystallites are too small to have continuous energy bands, even though a bulk crystal structure is present. The onset of such quantum properties sets a fundamental limit to device miniaturization in microelectronics5. Structures with either one, two or all three dimensions on the nanometer scale are of particular interest in solid state physics6. We report here our discovery of the biosynthesis of quantum crystallites in yeasts Candida glabrata and Schizosaccharomyces pombe, cultured in the presence of cad-mium salts. Short chelating peptides of general structure (γ-Glu-Cys)n-Gly control the nucleation and growth of CdS crystallites to peptide-capped intracellular particles of diameter 20 A. These quantum CdS crystallites are more monodisperse than CdS par-ticles synthesized chemically. X-ray data indicate that, at this small size, the CdS structure differs from that of bulk CdS and tends towards a six-coordinate rock-salt structure.

Biosynthesis of cadmium sulphide quantum semiconductor crystallites

We describe a high-temperature aerosol apparatus for the synthesis of 3-8-nm, surface-oxidized Si crystallites. The particles are made by homogeneous gas-phase nucleation following pyrolysis of dilute disilane in He. The particles are collected as a robust ethylene glycol colloid, and characterized by transmission electron microscopy, X-ray powder Brag scattering, IR, high-pressure liquid chromatography, and optical spectroscopy. The particles exhibit a shell structure, with a crystalline Si core, of bulk lattice constant, capped with an approximately 1.2-nm shell of silicon dioxide

A luminescent silicon nanocrystal colloid via a high-temperature aerosol reaction

Thermal sublimation of pure C60 and C70 has been used for depositing well‐characterized fullerene films on a variety of substrates. Film purity is determined by infrared absorption spectra and the extent of crystallinity of the face‐centered cubic structure by x rays. Thickness‐dependent optical and electrical measurements reveal uniform films over the thickness range 200–1000 A. We obtain optical absorption coefficients having values between those of Si and Ge and a relative permittivity having a value close to that of amorphous SiO2.

A. R. Kortan

Papers

Conducting films of C60 and C70 by alkali-metal doping

Nucleation and Growth of CdSe on ZnS Quantum Crystallite Seeds and Vice Versa, in Inverse Micelle Media

Biosynthesis of cadmium sulphide quantum semiconductor crystallites

A luminescent silicon nanocrystal colloid via a high-temperature aerosol reaction

Deposition and characterization of fullerene films