Experimental and Computational Studies of the Structure of CdSe Magic-Size Clusters.

Experimental and computational studies of resonant Raman spectra of truly monosized (CdSe)33 and (CdSe)34 nanoclusters have been performed. First-principles calculations of vibrations are performed to account for the peculiarity of the spectrum and resonant Raman selection rules. The calculation method is based on the analysis of the spatial distribution of the electron density in the ground and excited states and the corresponding displacement of atoms after the electronic transition. The calculated vibrational density of states and resonant Raman spectra of CdSe nanoclusters in a core-cage arrangement are distinctively different from those of small nanocrystals in the bulk fragment model and reasonably agree with the experimentally observed spectral features. The agreement can be considered as experimental evidence for the shell structure of "magic" CdSe nanoclusters. The resonant conditions for the Raman measurements and two different kinds of samples stabilized with decylamine in toluene and with cysteine in water ensure the reliability of our measurements and the minor influence of the stabilizer.

Synthesis of high concentration colloid solution of silica-coated AgI nanoparticles.

Methods for high concentration silica-coated silver iodide (AgI/SiO2) particles, which could be practically used as X-ray contrast agent, were examined. The first was a single-step method, which was to prepare AgI nanoparticles at an AgI concentration of 5 x 10(-3) M and coat the AgI nanoparticles with silica shell by a Stöber method. The second was a multiple-step method, which was to repeat a step for preparing a AgI/SiO2 particle colloid solution with 10(-3) M AgI 5 times for adjusting a final AgI concentration to 5 x 10(-3) M. In the two methods, dominant particle aggregation took place, though core-shell particles were also produced. The third was a salting-out method, which was to salt out AgI/SiO2 particles in their colloid solution prepared at an AgI concentration of 10(-3) M, remove supernatant by decantation, and redisperse the particles in a fresh solvent. Consequently, AgI/SiO2 particles with an AgI concentration as high as 0.05 M were successfully prepared with the salting-out method, and their core-shell structure was not damaged during the salting-out.

Control of shell thickness in silica-coating of Au nanoparticles and their X-ray imaging properties.

This paper describes a performance of precise control of shell thickness in silica-coating of Au nanoparticles based on a sol-gel process, and an investigation into X-ray imaging properties for the silica-coated Au (Au/SiO(2)) particles. The Au nanoparticles with a size of 16.9±1.2 nm prepared through a conventional citrate reduction method were used as core particles. The Au nanoparticles were silica-coated with a sol-gel reaction using tetraethylorthosilicate (TEOS) as a silica source, sodium hydroxide (NaOH) as a catalyst, and (3-aminopropyl) trimethoxysilane (APMS) as a silane coupling agent. An increase in TEOS concentration resulted in an increase in shell thickness. Under certain concentrations of Au, H(2)O, NaOH, and APMS, the Au/SiO(2) particles with silica shell thickness of 6.0-61.0 nm were produced with varying TEOS concentration. Absorption peak wavelength of surface plasmon resonance of the Au/SiO(2) colloid solution depended on silica shell thickness, which agreed approximately with the predictions by Mie theory. The as-prepared colloid solution could be concentrated up to an Au concentration of 0.19 M with salting-out and centrifugation. The concentrated colloid solution showed an X-ray image with high contrast, and a computed tomography value for the colloid solution with an Au concentration of 0.129 M was achieved 1329.7±52.7 HU.

Synthesis of silica-coated AgI nanoparticles and immobilization of proteins on them.

This paper describes a method for preparing silica-coated silver iodide (AgI/SiO2) particles and immobilizing proteins on the AgI/SiO2 particles. Colloid solution of AgI particles was prepared by mixing AgClO4 aqueous solution and KI aqueous solution. Silica-coating of the AgI particles was performed by adding 3-mercaptopropyltrimethoxysilane, tetraethylorthosilicate/ethanol solution and NaOH aqueous solution successively to the AgI colloid solution. TEM observation revealed that the AgI nanoparticles were coated with uniform silica shell. The AgI/SiO2 particles were surface-modified with 3-aminopropyltrimethoxysilane and succinic anhydride. It was confirmed by XPS measurement that amino group or carboxyl group was introduced onto the AgI/SiO2 particles. Protein-immobilization was performed in aqueous solution with bovine serum albumin (BSA) in the presence of the surface-modified AgI/SiO2 particles. UV-VIS absorption spectroscopy revealed that the BSA was adsorbed on the surface-modified particles.

Size-selective growth and stabilization of small CdSe nanoparticles in aqueous solution.

Using cysteine and its derivatives as capping molecules, we investigated the influence of the physical structure and chemical nature of capping molecules on the selective growth and stabilization of small CdSe nanoparticles (NPs) in aqueous solution at room temperature. Our investigations revealed specific roles for each functional group of cysteine, and we could correlate this structure and nature of the capping molecules with the size, size restriction, size distribution, and stability of the NPs. For selective growth and stabilization of the NPs in aqueous solution, their capping molecules should have at least one functional group with strong nucleophilicity as well as another free, charged functional group. Capping molecules acting as a monodentate ligand were more effective than those acting as a bidentate ligand for restricting the NPs to a smaller size, whereas the former was less effective than the latter for getting a narrower NP size distribution. Capping molecules with relatively bulky spatial geometry near the ligand-NP interface resulted in the formation of NPs with poor short- and long-term stabilities, whereas those having relatively compact spatial geometry near the interface led to NPs with at least moderate short-term stability. We saw that capping molecules having relatively compact outermost spatial geometry led to NPs with excellent long-term stability, whereas those having relatively bulky outermost spatial geometry produced NPs with at most only moderate long-term stability. Our results clearly showed general trends for the possibility of selective growth of stable semiconductor NPs with particular sizes in aqueous solution.

Aqueous-phase synthesis of ultra-stable small CdSe nanoparticles.

Very stable and small CdSe nanoparticles (NPs) were synthesized from the aqueous solutions containing L-cysteine (Cys) at room temperature. The Cys-capped CdSe NPs showed a very sharp excitonic peak at 420 nm. Its very small full width at half maximum (18 nm) indicates very high quality of the CdSe NPs. Their absorption features experienced little change over a month, implying an excellent stability of the CdSe NPs. The synthesis conditions were very critical to the optical property and stability of the CdSe NPs: only those prepared at specific conditions (n(Se-precursor)/n(Cd-precursor) = 0.25-0.5, n(Cys)/n(Cd-precursor) = approximately 9, pH = approximately 12) showed very sharp absorption peaks and maintained an excellent stability against time. Under these conditions, the peaks always appear at nearly the same wavelength, indicating that these NPs are selectively stable and grow at a particular size and structure.

Silicon subiodide clusters.

Silicon subiodide clusters (Si(n)I(m), n = 1-20) produced by laser ablation of bulk powder silicone tetraiodide have been investigated by time-of-flight mass spectroscopy and ab initio calculations. Both experimental results and theoretical calculations revealed a tendency to form different structures of the clusters depending on n: chain, ring, and cage structures for n < or = 6, 6 < n < 16, and n > or = 16, respectively. The results showed that iodine, like hydrogen, can be used for stable silicon cluster termination.

Concentrated colloids of silica-encapsulated gold nanoparticles: colloidal stability, cytotoxicity, and X-ray absorption.

As an effort to develop a new, effective, nontoxic X-ray contrast agent, the concentrated colloids of silica-encapsulated gold nanoparticles (Au@SiO2 NPs) were fabricated and their colloidal stability, cytotoxicity, and X-ray absorption were investigated. The concentrated colloidal NPs were manufactured by forming a 4 nm-thick silica shell on the surface of each Au NP with 15 nm diameter, followed by enrichment to [Au] = 100 mM. They were very stable in water: the NPs were well separated each other without forming agglomerates and their optical property was very similar to that before enrichment. The colloidal stability of the NPs in biological environment was strongly dependent on their previous morphology in water. The NPs with minor shell damage were stable in phosphate buffered saline (PBS) solution: both in water and in PBS solution, they showed very similar morphology and optical property. However, the NPs with profound shell damage formed big agglomerates in PBS solution, resulting in the red-shift and broadening of the Au surface plasmon resonance peak. Cell viability and proliferation assessments revealed the biocompatibility of the Au@SiO2 NPs: no apparent cytotoxicity was observed even at 100 ppm NPs. The concentrated colloidal NPs showed very strong X-ray absorption. Their relative X-ray transmittance to water was comparable to that of a commercial agent. Considering these, the concentrated colloids of the Au@SiO2 NPs are suitable for an X-ray contrast agent.

Monte Carlo calculation of second and third virial coefficients of small-scale comb polymers on lattice.

This paper reports the first computational estimation of the comb polymers' third virial coefficients. The number of the chains in the comb polymers range from 5 to 11. An algorithm that counts the contributing terms of the third virial coefficients in an accelerated manner is presented along with its efficiency dependence on the polymers' size. In addition, the second virial coefficients are estimated for the comb polymers and compared to previously reported results.

In situ surface-enhanced Raman scattering spectroelectrochemistry of oxygen species.

In situ surface-enhanced Raman scattering (SERS) combined with electrochemical analysis is applied to the determination of oxygen species on silver electrodes in alkaline hydroxide aqueous solution at room temperature and gold electrodes in carbonate melts at high temperature. This technique, referred to as SERS spectroelectrochemistry, reveals Raman spectral lines in the 500-1100 cm(-1) range under electrode potential scanning, assignable to superoxide ions (O2-) and peroxide ions (O2(2-)) on the electrode surface. These lines for oxygen molecule species have potential dependence with changing potential. In the alkaline hydroxide aqueous solution, the Raman peaks due to oxygen molecules are observed at potentials between 0.2 V and -0.8 V (vs. Ag/AgCl) only in the cathodic scan. This irreversible behavior in cyclic voltammograms indicates the existence of an intermediate stage in the oxygen reduction process, in which oxygen is released from the AgO films on the electrode at potentials corresponding to the onset of the last current peak in the voltammogram. This liberated oxygen molecule remains in solution at the interface until hydroxyls or water molecules are formed when the potential reaches the potential zero charge (PZC). In the high-temperature carbonate melts, Raman lines at 1047, 1080, and 800 cm(-1) are apparent for the eutectic (62 + 38) mol% (Li + K)CO3 melt at 923 K, and at 735 cm(-1) for the Li2CO3 melt at 1123 K. These results suggest that oxygen reduction in the Li2CO3 melt involves only peroxide ions, while that in (62 + 38) mol% (Li + K)CO3 involves both peroxide and superoxide ions at the three-phase boundary interface.

X-ray absorption of gold nanoparticles with thin silica shell.

Silica-coated gold (Au) nanoparticles were prepared and their morphological and X-ray absorption properties were investigated. These core-shell type nanoparticles are very stable in aqueous media and may be suitable for an X-ray contrast agent in biological systems. Transmission electron micrographs confirmed well-separated and relatively homogeneous morphology of the nanoparticles in highly concentrated colloids. Peak position for Au plasmon resonance was red-shifted with increasing shell thickness. X-ray absorption by the colloids of silica-coated Au nanoparticles was stronger than that by those of silica-coated Agl nanoparticles, a recently investigated X-ray contrast agent, at similar experimental conditions.

HREELS, STM, and STS study of CH(3)-terminated Si(111)-(1x1) surface.

An ideally (1x1)-CH(3)(methyl)-terminated Si(111) surface was composed by Grignard reaction of photochlorinated Si(111) and the surface structure was for the first time confirmed by Auger electron spectroscopy, low energy electron diffraction, high-resolution electron energy loss spectroscopy (HREELS), scanning tunneling microscopy (STM), and scanning tunneling spectroscopy (STS). HREELS revealed the vibration modes associated to the CH(3)-group as well as the C-Si bond. STM discerned an adlattice with (1x1) periodicity on Si(111) composed of protrusions with internal features, covering all surface terraces. The surface structure was confirmed to be stable at temperatures below 600 K. STS showed that an occupied-state band exists at gap voltage of -1.57 eV, generated by the surface CH(3) adlattice. This CH(3):Si(111)-(1x1) adlayer with high stability and unique electronic property is prospective for applications such as nanoscale lithography and advanced electrochemistry.

Ultra-stable nanoparticles of CdSe revealed from mass spectrometry.

Nanoparticles under a few nanometres in size have structures and material functions that differ from the bulk because of their distinct geometrical shapes and strong quantum confinement. These qualities could lead to unique device applications. Our mass spectral analysis of CdSe nanoparticles reveals that (CdSe)(33) and (CdSe)(34) are extremely stable: with a simple solution method, they grow in preference to any other chemical compositions to produce macroscopic quantities. First-principles calculations predict that these are puckered (CdSe)(28)-cages, with four- and six-membered rings based on the highly symmetric octahedral analogues of fullerenes, accommodating either (CdSe)(5) or (CdSe)(6) inside to form a three-dimensional network with essentially heteropolar sp(3)-bonding. This is in accordance with our X-ray and optical analyses. We have found similar mass spectra and atomic structures in CdS, CdTe, ZnS and ZnSe, demonstrating that mass-specified and macroscopically produced nanoparticles, which have been practically limited so far to elemental carbon, can now be extended to a vast variety of compound systems.

Hemocytes of Ciona intestinalis express multiple genes involved in innate immune host defense.

Ascidians, which are classified as urochordata, appear to employ a primitive system of host defense that is considered to be a prototype of vertebrate innate immunity. We performed a cDNA/EST study to identify the genes expressed in the hemocytes of Ciona intestinalis. We obtained 3357 one-path reads that were then grouped into 1889 independent clusters. Although two thirds of the clusters could not be assigned to any particular gene, the remaining 530 clusters had significant homology to genes with known function. Of these, 62 clusters appeared to be related to host defense mechanisms. These include transcripts whose products are probably involved in cytotoxicity, detoxification, inflammation, and apoptosis. As expected, elements of acquired immunity were not detected. Thus, Ciona hemocytes appear to express a number of host defense-related genes involved in innate immune mechanisms.