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Bovine serum albumin (BSA)-protected AgPt bimetallic nanoparticles have been synthesized through a galvanic replacement reaction, using a silver nanoprism as a template. Synthesis was performed without the use of synthetic chemical surfactants, using proteins as a surface coating. Structural and compositional characterizations were performed using several spectroscopic and microscopic techniques. The protein-protected AgPt nanoparticles show effective pH-switchable enzyme mimicking (“nanozyme”) activity similar to catalase and peroxidase. The platinum content in the AgPt nanoparticles is playing an important role in determining the enzymatic catalysis rate of the nanoparticles. Because of their porous structure, molecular payloads such as calcein also can be incorporated into the AgPt nanoparticles, which can be released on demand by chemical triggers, such as hydrogen peroxide.

Tin(II)sulfide (SnS) is a well-known representative of IV–VI semiconducting materials with a layered crystal structure. SnS is of great interest due to its low toxicity and its optical and electrical properties. Here, we report on the first colloidal synthesis of hexagonally shaped single crystalline SnS nanosheets with tunable dimensions. The SnS nanosheets crystallize in the thermodynamically preferred orthorhombic α-phase. High-resolution transmission electron microscopy and electron diffraction were executed in order to determine the growth direction of these hexagonally formed nanosheets. The simple hot-injection approach comprises the injection of a sulfur-oleylamine complex into a hot solution mixture containing oleylamine, oleic acid, tin(II)chloride, and hexamethyldisilazane (HMDS). HMDS is an essential chemical for many colloidal syntheses of two-dimensional nanosheets, but its function is not well described until now. Here, we elucidate the function of HMDS as an essential additive for the form...

The rise of two-dimensional (2D) graphene-cognated crystals with nonzero band gaps like transition metal dichalcogenides has led to a rapidly increasing interest in their dimensionality-dependent anisotropic properties, which bear high potential for ultrathin electronics. 2D crystals of the III–VI metal chalcogenide InSe represent a new kind of material class predestined for the use in optoelectronic applications as highly responsive photodetectors and field-effect transistors. We present a solution-processable method for 2D ultrathin InSe nanosheets (≤5 nm with ligands, lateral sizes up to ∼800 μm) with a detailed characterization of the sheet formation by a lamellar ligand templated growth. Optical and electrical transport properties, as well as in depth analysis of the crystal structure and stoichiometry of the colloidal nanosheets by electron and atomic force microscopy, X-ray photoelectron spectroscopy, and scattering methods complete this comprehensive study on a wet-chemical alternative to produce ...

We present a simple solution processed synthesis route for GaAs nanocrystals (NCs) with narrow size distribution and high crystallinity using wet chemical methods and commercially available inexpensive precursors with reduced toxicity. The reaction pathway can be described in three steps, starting with a transmetalation reaction between the gallium(III) halide precursor GaCl3 and the reduction agent n-butyllithium. At elevated temperatures elemental gallium is released in this process and enables the formation of GaAs NCs with magnesium arsenide (Mg3As2) as the arsenic source. We obtained a variety of different III–V semiconductor NCs including GaAs, InP, InAs, and GaP using this transmetalation reaction pathway.

We report a novel approach of seeded emulsion polymerization in which nanocrystals are used as seeds. Ultrasmall biocompatible polymer-coated nanocrystal with sizes between 15 and 110 nm could be prepared in a process that avoids any treatment with high shear forces or ultrasonication. The number of nanocrystals per seed, the size of the seeds, and the shell thickness can be independently adjusted. Single encapsulated nanocrystals in ultrasmall nanobeads as well as clusters of nanocrystals can be obtained. Polysorbat-80 was used as surfactant. It consists of poly(ethylene glycol) (PEG) chains, giving the particles outstanding biofunctional characteristics such as a minimization of unspecific interactions.

Gold nanostars are multibranched nanoparticles with sharp tips, which display extremely interesting plasmonic properties but require optimization. We present a systematic investigation of the influence of different parameters on the size, morphology, and monodispersity of Au nanostars obtained via seeded growth in concentrated solutions of poly(vinylpyrrolidone) in N,N-dimethylformamide. Controlled prereduction of Au(3+) to Au(+) was found to influence monodispersity (narrower plasmon bands), while the [HAuCl(4)]/[seed] molar ratio significantly affects the morphology and tip plasmon resonance frequency. We also varied the size of the seeds (2-30 nm) and found a clear influence on the final nanostar dimensions as well as on the number of spikes, while synthesis temperature notably affects the morphology of the particles, with more rounded morphologies formed above 60 °C. This rounding effect allowed us to confirm the importance of sharp tips on the optical enhancing behavior of these nanoparticles in surface-enhanced raman scattering (SERS). Additionally, the sensitivity toward changes in the local refractive index was found to increase for larger nanostars, though lower figure of merit (FOM) values were obtained because of the larger polydispersity.

Magnetic nanoparticles have been assembled into the bilayer membrane of block copolymer vesicles. The nanoparticles decorate the hydrophobic/hydrophilic interface, which leads to bridging of adjacent bilayers and the formation of oligo-lamellar vesicles. The nanoparticle uptake of the vesicles is sufficiently high to become magnetophoretic in external magnetic fields as shown by video microscopy.

A nonhydrolytic route to quantum-sized (d9 nm) ZnO nanocrystals in homogeneous organic solutions is presented. Nearly spherical ZnO nanocrystals were grown in a surfactant mixture of hexadecylamine and oleic acid (OLEA) by means of a two-step chemical process, based on the hot reduction (at 180-250 degrees C) of a zinc halide by superhydride (LiBEt3H) followed by oxidation of the resulting product. The experimental results suggested that the controlled growth of ZnO in the nanosized regime depended both on the OLEA-assisted generation of intermediate metallic nanoparticles and on the adjustment of their oxidation conditions by using a mild oxidant, trimethylamine-N-oxide, rather than molecular oxygen. The present synthetic approach demonstrates to be particularly suitable to prepare organic-soluble ultra-small ZnO nanocrystals of low size dispersion and of stable size, which are appealing for optoelectronic, catalytic, and sensing purposes.

We demonstrate that efficient shape control may be achieved in the shell of colloidally grown semiconductor nanocrystals (independent of the core), allowing the combination of a 0-D spherical CdSe core with a 1-D rodlike CdS shell. Besides exhibiting linearly polarized emission with a room-temperature quantum efficiency above 70%, these mixed-dimensionality colloidal heterostructures display large, length-dependent Stokes shifts as well as giant extinction coefficients approaching 107cm-1 M-1.

We report different approaches to the synthesis of size series of highly luminescent CdSe/CdS core−shell nanocrystals. The mixture of hexadecylamine (HDA)−trioctylphosphine oxide (TOPO)−trioctylphosphine (TOP) as stabilizing solvent was found to be very suitable for one-pot synthesis of nearly monodisperse CdSe nanocrystals followed by growing the CdS shell of a desired thickness. The obtained CdSe/CdS nanocrystals exhibited a narrow PL band (fwhm ∼27−35 nm) with reproducible room-temperature quantum yields as high as 50−85%. The emission color is tunable from green to red with increasing diameter of CdSe cores and/or thickness of the CdS shell. The possibility of preparing high-quality CdSe/CdS core−shell nanocrystals from the precursors cadmium acetate and H2S, which are more environmentally benign than conventional ones (e.g., dimethylcadmium) used in the organometallic synthesis of nanocrystals, was demonstrated. General aspects of the nanocrystal nucleation and growth as well as applicability of “gre...

New approaches to synthesize photostable thiol-capped CdTe nanocrystals are reported. Post-preparative size-selective precipitation and selective photochemical etching have been developed as methods providing an increase of photoluminescence quantum efficiency of the nanocrystals of up to 40%. Some advantages of thiol-capping in comparison to conventional organometallic syntheses of quantum dots are discussed.

Positively and negatively charged nanoparticles have been mixed together in order to obtain superlattice formation. The interaction between the particles was controlled by adjusting the ionic strength of the solutions. The self-assembly was studied with absorption spectroscopy, powder X-ray diffraction, and high-resolution transmission electron microscopy.

Highly luminescent CdTe nanocrystals were synthesized by reacting dimethylcadmium with different tellurium sources in mixtures of dodecylamine and trioctylphosphine as the coordinating and size-reg...

Nanocrystals of LaPO4:Eu and CePO4:Tb with a mean particle size of 5 nm and a narrow size distribution have been prepared by reacting the corresponding metal chlorides, phosphoric acid, and a base at 200 °C in tris(ethylhexyl) phosphate. Highly crystalline material was obtained as confirmed by X-ray powder diffraction measurements and high-resolution transmission electron microscopy. Successful doping with europium was evident from the splitting and the intensity pattern of the luminescence lines. Luminescence lifetime measurements were used to confirm doping and energy transfer in both materials. Colloidal solutions of CePO4:Tb exhibit an overall luminescence quantum yield of 16%.

We propose a new type of surfactants, namely, tetrazole derivatives which can be controllably removed from the nanoparticle surface. Tetrazoles are a peculiar class of heterocyclic compounds. The presence of four nitrogen atoms in the tetrazole ring determines their interesting physical and chemical properties. Tetrazoles show high thermal stability below 200C while decomposing at higher temperature with formation of gaseous products and no or very little solid residue. Moreover, the tetrazole group is known as an important ligand in coordination chemistry. Its donor nitrogen atoms can bind to various metal ions leading to stable complexes with diverse coordination modes of the heteroring. We report the synthesis of CdS NPs capped with 1-R-5-thiotetrazoles using two different synthetic schemes: solution-phase and solventless single precursor approaches. In both synthetic procedures cadmium thiotetrazolates were used as cadmium precursors and sources of surfactant., 4 pages, 3 figures, 2 schemes, 1 table

CdTe nanoclusters were prepared in aqueous solution by the reaction between Cd2+ and NaHTe in the presence of thioglycolic acid. Under reflux, the clusters start to crystallize and show a narrow band emission. The photoluminescence efficiency of CdTe nanocrystals strongly depends on the pH value of the colloidal solution. The maximum quantum yield at room temperature is approximately 18% when the pH value of the CdTe solution is brought to 4.5 by using thioglycolic acid. The optical spectroscopy studies imply that the pH-dependent behavior of the CdTe nanocrystals' fluorescence is caused by structural changes on the surface rather than the size of the nanocrystals. Systematic absorption and fluorescence studies on dialyzed samples suggest that in the acidic range a shell of cadmium thiol complexes is formed around the CdTe core. Thus, the fluorescence quantum yield is enhanced dramatically when the solution is made acidic. In contrast, such a shell can also be produced in the alkaline range, but only afte...

The wet chemical preparation, the electron microscopic characterization, and the temperature-dependent absorption as well as both the static and time-resolved fluorescence properties of Cd3P2 quantum dots are presented. The particles are strongly size quantized as seen from the 1.5 eV blue shift of the first electronic transition compared to the bulk bandgap of 0.5 eV. The particles emit close to the onset of absorption, exhibiting a quantum yield of 0.25 at room temperature. The luminescence decay has a multiexponential appearance at room temperature which transforms into two clearly distinguishable decay channels at low temperatures.