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We report on fluorescence quenching experiments of CdSe quantum dots, which were encapsulated for biocompatibility using different strategies. Since their fluorescence is very sensitive against water and other quenching molecules reaching their surface, quenching experiments allow conclusions on particle shielding towards the surrounding medium. It turns out that best shielded particles with comparable chemical composition of their ligand shell have also outstanding properties in respect of undesired unspecific cellular uptake. [ABSTRACT FROM AUTHOR]

A facile and safe ligand exchange method for readily synthesized CuInSe2 (CIS) and CuIn1-xGaxSe2 (CIGS) nanocrystals (NCs) from oleylamine to 1-ethyl-5-thiotetrazole, preserving the colloidal stability of the chalcopyrite structure, is presented. 1-Ethyl-5-thiotetrazole as thermally degradable ligand is adapted for the first time for trigonal pyramidal CIS (18 nm), elongated CIS (9 nm) and CIGS NCs (6 nm). Exchanged NC solutions are processed onto gold electrodes yielding ordered thin films. These films are thermally annealed at 260 °C to completely remove 1-ethyl-5-thiotetrazol leaving individual closely assembled NCs with virtually bare surfaces. The current-voltage characteristics of the NC solids are measured prior to ligand thermolysis in the dark and under illumination and after ligand thermolysis in the same manner. The conductivity of trigonal pyramidal CIS increases by four orders of magnitude (1.4 × 10−9 S cm−1 (dark) to 1.4 × 10−5 S cm−1 (illuminated)) for ligand-free NC films. Elongated CIS NC films show a three orders of magnitude conductivity increase and CIGS NC films exhibit improved conductivity by two orders of magnitude. Conductivity enhancement thereby depends on the NC size accentuating the role of trap-states and internal grain boundaries in ligand-free NC solids for electrical transport. This approach for the first time offers the possibility to address chalcopyrite materials' electrical properties in a virtually ligand-free state. [ABSTRACT FROM AUTHOR]

Semiconductor quantum dots and superparamagnetic iron oxide nanocrystals have physical properties that are well suited for biomedical imaging. Previously, we have shown that iron oxide nanocrystals embedded within the lipid core of micelles show optimized characteristics for quantitative imaging. Here, we embed quantum dots and superparamagnetic iron oxide nanocrystals in the core of lipoproteins—micelles that transport lipids and other hydrophobic substances in the blood—and show that it is possible to image and quantify the kinetics of lipoprotein metabolism in vivo using fluorescence and dynamic magnetic resonance imaging. The lipoproteins were taken up by liver cells in wild-type mice and displayed defective clearance in knock-out mice lacking a lipoprotein receptor or its ligand, indicating that the nanocrystals did not influence the specificity of the metabolic process. Using this strategy it is possible to study the clearance of lipoproteins in metabolic disorders and to improve the contrast in clinical imaging. [ABSTRACT FROM AUTHOR]

Bringing together compounds of intrinsically different functionality, such as inorganic nanostructures and organic molecules, constitutes a particularly powerful route to creating novel functional devices with synergetic properties found in neither of the constituents. We introduce nanophotonic functional elements combining two classes of materials, semiconductor nanocrystals and dyes, whose physical nature arises as a superposition of the properties of the individual components. The strongly absorbing rod-like nanocrystals focus the incident radiation by photopumping the weakly absorbing dye via energy transfer. The CdSe/CdS nanorods exhibit a large quantum-confined Stark effect on the single-particle level, which enables direct control of the spectral resonance between donor and acceptor required for nanoscopic Förster-type energy transfer in single nanorod–dye couples. With this far-field manipulation of a near-field phenomenon, the emission from single dye molecules can be controlled electrically. We propose that this effect could lead to the design of single-molecule optoelectronic switches providing building blocks for more complex nanophotonic circuitry. [ABSTRACT FROM AUTHOR]

Abstract Mechanical properties and local martensitic phase transformation of individual nanocrystalline zirconia microspheres were assessed by complementary (in situ) electron microscopy techniques. Particles were deformed by compression in a SEM and the local structure was determined by ex situ SAED of a FIB prepared lamella. The local texture and amount of transformed grains can be explained by a continuum-like behavior modelled by FEM calculations: The phase transformation is found for grains which are preferentially oriented with respect to the deviatoric stresses and show the rotation of the maximum shear stress during the experiment. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

We report a novel approach of seeded emulsion polymerizationin which nanocrystals are used as seeds. Ultrasmall biocompatiblepolymer-coated nanocrystal with sizes between 15 and 110 nm couldbe prepared in a process that avoids any treatment with high shearforces or ultrasonication. The number of nanocrystals per seed, thesize of the seeds, and the shell thickness can be independently adjusted.Single encapsulated nanocrystals in ultrasmall nanobeads as well asclusters of nanocrystals can be obtained. Polysorbat-80 was used assurfactant. It consists of poly(ethylene glycol) (PEG) chains, givingthe particles outstanding biofunctional characteristics such as aminimization of unspecific interactions. [ABSTRACT FROM AUTHOR]

Abstract: Biodegradable poly-(D,L-lactide-co-glycolide) microspheres (PLGA-MS) are approved as a drug delivery system in humans and represent a promising antigen delivery device for immunotherapy against cancer. Immune responses following PLGA-MS vaccination require cross-presentation of encapsulated antigen by professional antigen presenting cells (APCs). While the potential of PLGA-MS as vaccine formulations is well established, the intracellular pathway of cross-presentation following phagocytosis of PLGA-MS is still under debate. A part of the controversy stems from the difficulty in unambiguously identifying PLGA-MS within cells. Here we show a novel strategy for the efficient encapsulation of inorganic nanocrystals (NCs) into PLGA-MS as a tool to study their intracellular localization. We microencapsulated NCs as an electron dense marker to study the intracellular localization of PLGA-MS by transmission electron microscopy (TEM) and as fluorescent labels for confocal laser scanning microscopy. Using this method, we found PLGA-MS to be rapidly taken up by dendritic cells and macrophages. Co-localization with the lysosomal marker LAMP1 showed a lysosomal storage of PLGA-MS for over two days after uptake, long after the initiation of cross-presentation had occurred. Our data argue against an escape of PLGA-MS from the endosome as has previously been suggested as a mechanism to facilitate cross-presentation of PLGA-MS encapsulated antigen. [Copyright &y& Elsevier]

The article focuses on the mechanism behind cadmium sulfide nanoparticles' (NP) attachment to carbon nanotubes following the hot injection method. According to the authors, the presence of water improves the nanotube coverage while DCE, hydrochloride, or in general chloride, is responsible for the shape transformation of the NPs.

GaAs nanocrystals with narrow size distribution and high crystallinity are synthesized by addition of n-butyllithium in hexane to a mixture of GaCl3 and Mg3As2 using tri-n-octylphosphine oxide as stabilizing agent and 1-octadecene as solvent (N2, 315 °C, 90 min). [ABSTRACT FROM AUTHOR]