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The pyrolytic synthesis of homogeneously alloyed Cd[S.sub.x][Se.sub.1-x] nanocrystals in all proportions using a single synthetic method and the characterization of the nanocrystals to determine the structure, size and composition are reported. The band gap of these nanocrystals can be tuned by size or by composition and its dependence on alloy composition is found to be slightly nonlinear.

Research has been conducted on the ligand-conjugated nanocrystals. The use of these ligands in targeting cell surface receptors, transporters and ion channels has been investigated via the interactions of serotonin-labeled CdSe nanocrystals with the antidepressant-sensitive transporters expressed in HeLa and HEK-293 cells and the results are described.

The first images of the structure of white-light emitting ultrasmall CdSe nanocrystals are obtained by using aberration-corrected atomic number contrast scanning transmission electron microscopy (Z-STEM). The exciton dynamics are measured at different wavelengths of the white-light spectrum by using ultrafast fluorescence upconversion spectroscopy, which has suggested that a myriad of trap states are responsible for the broad-spectrum emission.

A number of thiols carrying a substituted cinnamate tail were synthesized to examine the photochemical properties of organic ligands on the surface of nanocrystalline (NC) CdSe particles. The NCs have dramatically increased aerobic photoinstability as compared to NC without cinnamate ligands since the surface cinnamate facilitates electron transfer from excited NC* to [O.sub.2] in solution by acting as an electron carrier.

The potential usefulness of pyrolytically grown magic-sized cadmium selenide (CdSe) nanocrystals as a white-light phosphor is presented. The ultra-small nanocrystals exhibit a strong Stokes shift and broad emission covering the entire visible spectrum, which provides the ideal platform to study the nanocrystal-molecule transition.

Functionalization of highly fluorescent CdSe/ZnS core-shell nanocrystals (quantum dots, qdots) is an emerging technology for labeling cell surface proteins. We have synthesized a conjugate consisting of ∼150–200 muscimols (a GABA receptor agonist) covalently joined to the qdot via a poly(ethylene glycol) (PEG) linker (∼78 ethylene glycol units) and investigated the binding of this muscimol-PEG-qdot conjugate to homomeric ρ1 GABAc receptors expressed in Xenopus oocytes. GABAc receptors mediate inhibitory synaptic signaling at multiple locations in the central nervous system (CNS). Binding of the conjugate was analyzed quantitatively by determining the fluorescence intensity of the oocyte surface membrane in relation to that of the surrounding incubation medium. Upon 5- to 10-min incubation with muscimol PEG-qdots (34 nM in qdot concentration), GABAc-expressing oocytes exhibited a fluorescent halo at the surface membrane that significantly exceeded the fluorescence of the incubation medium. This halo was absent following muscimol-PEG-qdot treatment of oocytes lacking GABAc receptors. Incubation of the oocyte with free muscimol (100 μM-5 mM). PEG-muscimol (500 μM), or GABA (100 μM 5 mM) substantially reduced or eliminated the fluorescence halo produced by muscimol-PEG-qdots, and the removal of GABA or free muscimol led to a recovery of muscimol PEG-qdot binding. Unconjugated qdots and PEG-qdots that lacked conjugated muscimol neither exhibited significant binding activity nor diminished the subsequent binding of muscimol-PEG-qdots. The results indicate that muscimol joined to qdots via a long-chain PEG linker exhibits specific binding activity at the ligand-binding pocket of expressed GABAc receptors, despite the presence of both the long PEG linker and the sterically bulky qdot. [ABSTRACT FROM AUTHOR]

Alloy nanocrystals provide an additional degree of freedom in selecting desirable properties for nanoscale engineering because their physical and optical properties depend on both size and composition. We report the pyrolytic synthesis of homogeneously alloyed CdSxSe1-x nanocrystals in all proportions. The nanocrystals are characterized using UV-visible absorption spectroscopy, transmission electron microscopy, X-ray diffractrometry, and Rutherford backscattering spectrometry to determine precisely structure, size, and composition. The dependence of band gap on nanocrystal size and composition is elucidated, yielding a bowing constant of 0.29, in agreement with bulk values. In addition, the morphology of the resultant nanocrystals can be altered by changing the reaction conditions, generating structures ranging from homogeneous, spherical nanocrystals to one-dimensional gradient nanorods. [ABSTRACT FROM AUTHOR]