Feng Teng

Facile One-Step Synthesis and Transformation of Cu(I)-Doped Zinc Sulfide Nanocrystals to Cu1.94S–ZnS Heterostructured Nanocrystals

A facile one-pot heating process without any injection has been developed to synthesize different Cu-Zn-S-based nanocrystals. The composition of the products evolves from Cu(I)-doped ZnS (ZnS:Cu(I)) nanocrystals into heterostructured nanocrystals consisting of monoclinic Cu1.94S and wurtzite ZnS just by controlling the molar ratios of zinc acetylacetonate (Zn(acac)2) to copper acetylacetonate (Cu(acac)2) in the mixture of n-dodecanethiol (DDT) and 1-octadecene (ODE). Accompanying the composition transformation, the crystal phase of ZnS is changed from cubic zinc blende to hexagonal wurtzite. Depending on the synthetic parameters including the reaction time, temperature, and the feeding ratios of Zn/Cu precursors, the morphology of the as-obtained heterostructured nanocrystals can be controlled in the forms of taper-like, matchstick-like, tadpole-like, or rod-like. Interestingly, when the molar ratio of Cu(acac)2 to Zn(acac)2 is increased to 9:1, the crystal phase of the products is transformed from monoclinic Cu1.94S to the mixed phase composed of cubic Cu1.8S and tetragonal Cu1.81S as the reaction time is further prolonged. The crystal-phase transformation results in the morphological change from quasi-spherical to rice shape due to the incorporation of Zn ions into the Cu1.94S matrix. This method provides a simple but highly reproducible approach for synthesis of Cu(I)-doped nanocrystals and heterostructured nanocrystals, which are potentially useful in the fabrication of optoelectronic devices.

Biocompatible fluorescent core–shell nanoparticles for ratiometric oxygen sensing

Ratiometric fluorescent core–shell nanoparticles (NPs) with good biocompatibility are successfully prepared by a one-step reprecipitation–encapsulation method for sensing dissolved oxygen. The particle core comprises the oxygen probe platinum(II) octaethylporphine (PtOEP), the reference dye coumarin 6 (C6) and a third fluorophore dinaphthoylmethane (DNM). Upon single 381 nm excitation, C6 gives oxygen-insensitive referenced green fluorescence via intraparticle FRET from DNM, whilst PtOEP yields highly oxygen-sensitive red phosphorescence with a quenching response of 94%. The fluorescence quenching of the NPs against oxygen follows a linear Stern–Volmer behavior, which is fundamental for practical sensing. Moreover, positively charged poly-L-lysine molecules are in situ self-assembled onto the surface of NPs during synthesis. The resultant core–shell NPs with functional groups exhibit low cytotoxic effects as well as effortless cellular uptake, indicating targeted intracellular oxygen sensing is very promising using the oxygen nanosensors.

Upconversion multicolor tuning: Red to green emission from Y2O3:Er, Yb nanoparticles by calcination

In this paper, we report the color tuning of Er and Yb codoped Y2O3 upconversion materials by calcination within a fixed doping concentration under the excitation of 980u2009nm semiconductor laser diode. By introducing the defects through use of a surfactant (cetyltrimethylammonium bromide) and removing the defects by changing the calcination temperature, the green emission (2H11/2, 4S3/2→4I15/2) and red emission (4F9/2→4I15/2) of Er ions were enhanced selectively, thus the color output could be tuned from red to green. It is expected that these color-tuned materials have great potential for applications in multiplexed labeling.

Poly-L-lysine assisted synthesis of core–shell nanoparticles and conjugation with triphenylphosphonium to target mitochondria

In this paper, we report a facile route to synthesize mitochondria-targeted core-shell nanoparticles (NPs). Firstly, PLL-coated NPs are prepared by a one-step reprecipitation-encapsulation method assisted by positively charged poly-l-lysine (PLL). The effect of the molecular weight of PLL on the formation of particles is studied in terms of morphology, size and zeta potential, and medium-sized PLL (MH-PLL) is proved to be the optimum one. By means of crosslinking with different amounts of glutaraldehyde, amino groups in MH-PLL-NPs are characterized by zeta potential and fluorescamine assay, respectively. The results indicate that in the PLL shell, only a small portion of amino groups (surface amino groups, SAGs) are available for conjugation, while the other groups exclusively contribute to zeta potential. Subsequently, a known mitochondriotropic ligand, triphenylphosphonium (TPP), is conjugated with SAG via a carbodiimide reaction, which is evaluated by NMR and absorption spectra, respectively. The TPP-MH-PLL-NPs exhibit a low cytotoxic effect tested by the MTT method, as well as efficient cellular uptake microscopically observed after a fluorescent dye, coumarin 6, is incorporated. Most importantly, the TPP-conjugated NPs can selectively target mitochondria, demonstrated by the merged z-stacked images in co-localization experiments with MitoTracker-stained mitochondria. Given that many hydrophobic species could be loaded into the particle core, TPP-MH-PLL-NPs are very promising as mitochondria-targeted nanocarriers for imaging or anti-cancer therapies.

Shape-controlled synthesis of PbS nanocrystals via a simple one-step process.

A one-step colloidal process was adopted to prepare face-centered-cubic PbS nanocrystals with different shapes such as octahedral, starlike, cubic, truncated octahedral, and truncated cubic. The features of this approach avoid the presynthesis of any organometallic precursor and the injection of a toxic phosphine agent. A layered intermediate compound (lead thiolate) forms in the initial stage of the reaction, which effectively acts as the precursor to decompose into the PbS nanocrystals. The size and shape of the PbS nanocrystals can be easily controlled by varying the reaction time, the reactant concentrations, the reaction temperatures, and the amount of surfactants. In particular, additional surfactants other than dodecanethiol, such as oleylamine, oleic acid, and octadecene, play an important role in the shape control of the products. The possible formation mechanism for the PbS nanocrystals with various shapes is presented on the basis of the different growth directions of the nanocrystals with the assistance of the different surfactants. This method provides a facile, low-cost, highly reproducible process for the synthesis of PbS nanocrystals that may have potential applications in the fabrication of photovoltaic devices and photodetectors.

Synthesis of ratiometric fluorescent nanoparticles for sensing oxygen

AbstractA facile reprecipitation-encapsulation method is used for the preparation of ratiometric fluorescent nanoparticles (NPs) for sensing intracellular oxygen. The surface of the NPs is modified in-situ with poly-L-lysine, which renders good biocompatibility and enables easy internalization into living cells. The sensor NPs contain a red fluorescent probe whose fluorescence is sensitive to oxygen with a quenching response of 77 % on going from nitrogen saturation to oxygen saturation, and a reference dye giving a green signal that acts as an oxygen-independent reference. The ratio of the two emissions serves as the analytical information and is sensitive to dissolved oxygen in the 0–43xa0ppm concentration range. When incorporated into cells, the ratio of the signals increases by 400xa0% on going from oxygen-saturated to oxygen-free environment.n FigureDissolved oxygen could be visually detected using the ratiometric nanoparticles. Under single-wavelength excitation, red fluorescence is highly sensitive to oxygen, whereas green fluorescence keeps constantly.

Controllable synthesis of silver and silver sulfide nanocrystals via selective cleavage of chemical bonds

A one-step colloidal process has been adopted to prepare silver (Ag) and silver sulfide (Ag₂S) nanocrystals, thus avoiding presynthesis of an organometallic precursor and the injection of a toxic phosphine agent. During the reaction, a layered intermediate compound is first formed, which then acts as a precursor, decomposing into the nanocrystals. The composition of the as-obtained products can be controlled by selective cleavage of S-C bonds or Ag-S bonds. Pure Ag₂S nanocrystals can be obtained by directly heating silver acetate (Ag(OAc)) and n-dodecanethiol (DDT) at 200u2009° C without any surfactant, and pure Ag nanocrystals can be synthesized successfully if the reaction temperature is reduced to 190u2009° C and the amount of DDT is decreased to 1 ml in the presence of a non-coordinating organic solvent (1-octadecene, ODE). Otherwise, the mixture of Ag and Ag₂S is obtained by directly heating Ag(OAc) in DDT by increasing the reaction temperature or in a mixture of DDT and ODE at 200u2009° C. The formation mechanism has been discussed in detail in terms of selective S-C and Ag-S bond dissociation due to the nucleophilic attack of DDT and the lower bonding energy of Ag-S. Interestingly, some products can easily self-assemble into two- or three-dimensional (2D or 3D) highly ordered superlattice structures on a copper grid without any additional steps. The excess DDT plays a key role in the superlattice structure due to the bundling and interdigitation of the thiolate molecules adsorbed on the as-obtained nanocrystals.

Improvement of amplified spontaneous emission performance of conjugated polymer waveguides with a low loss cladding

We report the improvement of the amplified spontaneous emission (ASE) performance in the optically pumped symmetric thin film waveguide glass/indium-tin oxide (ITO)/SiO2/poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene]/SiO2/Al or Ag by optimizing the thickness of SiO2 and replacing the Al electrode with Ag, where SiO2 acted as a spacer layer to prevent the ASE at 620u2009nm from being destructed. The results show that the SiO2/Ag cladding reduced the ASE threshold to 4u2009μJ/pulse compared with the SiO2/Al cladding, owing to the higher work function and reflection rate as well as lower absorption loss of the Ag electrode. No photoluminescence at 580u2009nm being observed makes it possible for an electric field to only modulate the ASE at 620u2009nm in the device with the SiO2/Ag cladding. The electric-field quenching of the ASE has been observed, which increases with the electric field. The field dependence of ASE can be attributed to field-induced dissociation of photogenerated excitons in the polymer waveguides.

Sensing water in organic solvent using a polyurethane-silica hybrid membrane doped with a luminescent ruthenium complex

AbstractWe have prepared an ~1.4xa0μm thin hybrid film from polyurethane (PU) hydrogel and tetraethylorthosilicate (TEOS) by a sol–gel method, and have incorporated the red-luminescent ruthenium-tris-bipyridyl complex. At an optimized ratio of PU/TEOS (1.5:1; w/w) and annealing temperature (60xa0°C), the membrane sensor exhibits good capability to extract water from organic solvents but also can well retain the ruthenium dye. If contacted with water-containing organic solvents such as acetone or THF, both the luminescence intensity and wavelength change significantly. The response of luminescence intensity to the water fraction in organics is sigmoidal, which can be well fitted with a modified Stern-Volmer equation. The sensor works in the ranges of 0–6xa0% and 0–12xa0% (v/v) of water in acetone and THF, respectively, with detection limits of 0.13xa0% and 0.486xa0% (v/v).n FigureA ultrathin Ru(bpy)32+-doped hybrid film (~1.4xa0μm) prepared from PU hydrogel and TEOS shows water-dependent luminescence in both intensity and emission energy when calibrated in organic solvents.