Sacrificial Silver Nanoparticles: Reducing GeI2 To Form Hollow Germanium Nanoparticles by Electroless Deposition.

Herein we report the electroless deposition of Ge onto sacrificial Ag nanoparticle (NP) templates to form hollow Ge NPs. The formation of AgI is a necessary component for this reaction. Through a systematic study of surface passivating ligands, we determined that tri-n-octylphosphine is necessary to facilitate the formation of hollow Ge NPs by acting as a transport agent for GeI2 and the oxidized Ag(+) cation (i.e., AgI product). Annular dark-field (ADF) scanning transmission electron microscopy (STEM) imaging of incomplete reactions revealed Ag/Ge core/shell NPs; in contrast, completed reactions displayed hollow Ge NPs with pinholes which is consistent with the known method for dissolution of the nanotemplate. Characterization of the hollow Ge NPs was performed by transmission electron microscopy, ADF-STEM, energy-dispersive X-ray spectroscopy, UV-vis spectrophotometry, and Raman spectroscopy. The galvanic replacement reaction of Ag with GeI2 offers a versatile method for controlling the structure of Ge nanomaterials.

Chemical insight into the origin of red and blue photoluminescence arising from freestanding silicon nanocrystals.

Silicon nanocrystals (Si NCs) are attractive functional materials. They are compatible with standard electronics and communications platforms and are biocompatible. Numerous methods have been developed to realize size-controlled Si NC synthesis. While these procedures produce Si NCs that appear identical, their optical responses can differ dramatically. Si NCs prepared using high-temperature methods routinely exhibit photoluminescence agreeing with the effective mass approximation (EMA), while those prepared via solution methods exhibit blue emission that is somewhat independent of particle size. Despite many proposals, a definitive explanation for this difference has been elusive for no less than a decade. This apparent dichotomy brings into question our understanding of Si NC properties and potentially limits the scope of their application. The present contribution takes a substantial step forward toward identifying the origin of the blue emission that is not expected based upon EMA predictions. It describes a detailed comparison of Si NCs obtained from three of the most widely cited procedures as well as the conversion of red-emitting Si NCs to blue emitters upon exposure to nitrogen-containing reagents. Analysis of the evidence is consistent with the hypothesis that the presence of trace nitrogen and oxygen even at the parts per million level in Si NCs gives rise to the blue emission.

Development of iron-doped silicon nanoparticles as bimodal imaging agents.

We demonstrate the synthesis of water-soluble allylamine-terminated Fe-doped Si (Si(xFe)) nanoparticles as bimodal agents for optical and magnetic imaging. The preparation involves the synthesis of a single-source iron-containing precursor, Na(4)Si(4) with x% Fe (x = 1, 5, 10), and its subsequent reaction with NH(4)Br to produce hydrogen-terminated Si(xFe) nanoparticles. The hydrogen-capped nanoparticles are further terminated with allylamine via thermal hydrosilylation. Transmission electron microscopy indicates that the average particle diameter is ∼3.0 ± 1.0 nm. The Si(5Fe) nanoparticles show strong photoluminescence quantum yield in water (∼10%) with significant T(2) contrast (r(2)/r(1) value of 4.31). Electron paramagnetic resonance and Mössbauer spectroscopies indicate that iron in the nanoparticles is in the +3 oxidation state. Analysis of cytotoxicity using the resazurin assay on HepG2 liver cells indicates that the particles have minimal toxicity.

Surface functionalization of mesoporous silica nanoparticles controls loading and release behavior of mitoxantrone.

PURPOSE: To investigate the effect of surface functionalization of mesoporous silica nanoparticles (MSN) on crystallization, loading, release and activity of mitoxantrone (MTX). METHODS: Thiol-, amine-, and mixed thiol/amine-functionalized MSN were synthesized and characterized by electron microscopy, thermogravimetry, surface area analysis, elemental analysis and zeta potential. MTX loading and release kinetics were determined in phosphate and acetate buffers (pH 7.4 and 4.5). The crystalline state of MTX in MSN was determined by differential scanning calorimetry and X-ray diffraction. Cytotoxicity and activity of MTX loaded MSN were determined by MTS assay in MDA-MB-231 cells. RESULTS: Our results demonstrate that loading of MTX depends strongly on the type of surface functional groups in MSN. Thiol-MSN showed the highest MTX loading (18 % w/w) when compared with thiol/amine-MSN (6 % w/w) and amine-MSN (1 % w/w). MTX release was strongly dependent on the pH of the release medium and the type of surface functional group. MTX was found in the amorphous form when loaded in thiol-functionalized MSN. No significant effect of surface modification of MSN on particle toxicity was observed. MTX loaded in MSN exhibited comparable anticancer activity in vitro as free MTX. CONCLUSION: Surface modifications of MSN have significant effect on MTX crystallization and release behavior.

Solid-state phase transformations in solution: templated conversion of nanoscale nickel phosphides.

Conversion of Ni(12)P(5) nanoparticles to Ni(2)P is demonstrated to occur via a solid-state, rather than a solution dissolution, process. The templated transformation is employed to make monodisperse hollow or solid particles of the catalytically active phase Ni(2)P with surface areas of ~17 m(2) g(-1).

Synthetic levers enabling independent control of phase, size, and morphology in nickel phosphide nanoparticles.

Simultaneous control of phase, size, and morphology in nanoscale nickel phosphides is reported. Phase-pure samples of discrete nanoparticles of Ni12P5 and Ni2P in hollow and solid morphologies can be prepared in a range of sizes (10-32 nm) by tuning key interdependent synthetic levers (P:Ni precursor ratio, temperature, time, oleylamine quantity). Size and morphology are controlled by the P:Ni ratio in the synthesis of the precursor particles, with large, hollow particles formed at low P:Ni and small, solid particles formed at high P:Ni. The P:Ni ratio also impacts the phase at the crystallization temperature (300-350 °C), with metal-rich Ni12P5 generated at low P:Ni and Ni2P at high P:Ni. Moreover, the product phase formed can be decoupled from the initial precursor ratio by the addition of more "P" at the crystallization temperature. This enables formation of hollow particles (favored by low P:Ni) of Ni2P (favored by high P:Ni). Increasing temperature and time also favor formation of Ni2P, by generating more reactive P and providing sufficient time for conversion to the thermodynamic product. Finally, increasing oleylamine concentration allows Ni12P5 to be obtained under high P:Ni precursor ratios that favor solid particle formation. Oleylamine concentration also acts to "tune" the size of the voids in particles formed at low P:Ni ratios, enabling access to Ni12P5 particles with different void sizes. This approach enables an unprecedented level of control over phase and morphology of nickel phosphide nanoparticles, paving the way for systematic investigation of the impact of these parameters on hydrodesulfurization activities of nickel phosphides.

Oxidation does not (always) kill reactivity of transition metals: solution-phase conversion of nanoscale transition metal oxides to phosphides and sulfides.

Unexpected reactivity on the part of oxide nanoparticles that enables their transformation into phosphides or sulfides by solution-phase reaction with trioctylphosphine (TOP) or sulfur, respectively, at temperatures of ≤370 °C is reported. Impressively, single-phase phosphide products are produced, in some cases with controlled anisotropy and narrow polydispersity. The generality of the approach is demonstrated for Ni, Fe, and Co, and while manganese oxides are not sufficiently reactive toward TOP to form phosphides, they do yield MnS upon reaction with sulfur. The reactivity can be attributed to the small size of the precursor particles, since attempts to convert bulk oxides or even particles with sizes approaching 50 nm were unsuccessful. Overall, the use of oxide nanoparticles, which are easily accessed via reaction of inexpensive salts with air, in lieu of organometallic reagents (e.g., metal carbonyls), which may or may not be transformed into metal nanoparticles, greatly simplifies the production of nanoscale phosphides and sulfides. The precursor nanoparticles can easily be produced in large quantities and stored in the solid state without concern that "oxidation" will limit their reactivity.

Enhanced gene and siRNA delivery by polycation-modified mesoporous silica nanoparticles loaded with chloroquine.

PURPOSE: To prepare mesoporous silica-based delivery systems capable of simultaneous delivery of drugs and nucleic acids. METHODS: The surface of mesoporous silica nanoparticles (MSN) was modified with poly(ethylene glycol) (PEG) and poly(2-(dimethylamino)ethylmethacrylate) (PDMAEMA) or poly(2-(diethylamino)ethylmethacrylate) (PDEAEMA). The particles were then loaded with a lysosomotropic agent chloroquine (CQ) and complexed with plasmid DNA or siRNA. The ability of the synthesized particles to deliver combinations of CQ and nucleic acids was evaluated using luciferase plasmid DNA and siRNA targeting luciferase and GAPDH. RESULTS: The results show a slow partial MSN dissolution to form hollow silica nanoparticles in aqueous solution. The biological studies show that polycation-modified MSN are able to simultaneously deliver CQ with DNA and siRNA. The co-delivery of CQ and the nucleic acids leads to a significantly increased transfection and silencing activity of the complexes compared with MSN not loaded with CQ. CONCLUSION: PEGylated MSN modified with polycations are promising delivery vectors for combination drug/nucleic acid therapies.

Control of phase in phosphide nanoparticles produced by metal nanoparticle transformation: Fe2P and FeP.

The transformation of Fe nanoparticles by trioctylphosphine (TOP) to phase-pure samples of either Fe(2)P or FeP is reported. Fe nanoparticles were synthesized by the decomposition of Fe(CO)(5) in a mixture of octadecene and oleylamine at 200 degrees C and were subsequently reacted with TOP at temperatures in the region of 350-385 degrees C to yield iron phosphide nanoparticles. Shorter reaction times favored an iron-rich product (Fe(2)P), and longer reaction times favored a phosphorus-rich product (FeP). The reaction temperature was also a crucial factor in determining the phase of the final product, with higher temperatures favoring FeP and lower temperatures Fe(2)P. We also observe the formation of hollow structures in both FeP spherical nanoparticles and Fe(2)P nanorods, which can be attributed to the nanoscale Kirkendall effect. Magnetic measurements conducted on phase-pure samples suggest that approximately 8 x 70 nm Fe(2)P rods are ferromagnetic with a Curie temperature between 215 and 220 K and exhibit a blocking temperature of 179 K, whereas FeP is metamagnetic with a Neel temperature of approximately 120 K. These data agree with the inherent properties of bulk-phase samples and attest to the phase purity that can be achieved by this method.