Esterification-Induced Spontaneous Deposition of Nanoparticle Monolayers on Substrates with Percolation Network Morphology.

Nanoparticle monolayers (NPMLs) exhibit unique collective properties that are highly desirable for applications in sensors, catalysts, and optics. However, their practical use is often hindered by structural instability, especially when they are exposed to solvents. In this study, we developed a method for the spontaneous deposition of gold nanoparticle monolayers (AuNPMLs) on silicon substrates via covalent bonding interactions that provides excellent structural stability in solvents with varying polarities. The esterification reaction between carboxyl-functionalized gold nanoparticles and alkyl-chloride-functionalized silicon substrates spontaneously forms AuNPMLs on the substrate in which single-crystalline domains are interconnected, forming a percolation network morphology. The ex situ scanning electron microscopy measurements show that the surface coverage of AuNPMLs rapidly increases up to ca. 60% during the initial 10 min, followed by gradual growth and saturation at ca. 70% at 360 min of deposition time. On the other hand, the single-crystalline domain size reaches its maximum at 45 min and then gradually decreases, which may be attributed to the desorption of AuNPs by the hydrolysis of ester bonds. The reflectance spectra of AuNPMLs showed the red shift as the deposition time increases up to 45 min with a subsequent blue shift thereafter, which is consistent with the change of the single-crystalline domain size with the deposition time. The covalent bonding interaction-mediated nanoparticle deposition method can be used to form stable AuNPMLs with controlled surface coverage and domain size, allowing for fine control of the optical properties and possibly other properties. The excellent structural stability of AuNPMLs and their controlled properties may provide new opportunities for practical applications of NPMLs.

Spontaneous Formation of Highly Stable Nanoparticle Supercrystals Driven by a Covalent Bonding Interaction.

Nanoparticle supercrystals (NPSCs) are of great interest as materials with emergent properties. Different types of intermolecular forces, such as van der Waals interaction and hydrogen bonding, are present in the NPSCs fabricated to date. However, the limited structural stability of such NPSCs that results from the weakness of these intermolecular forces is a challenge. Here, we report a spontaneous formation of NPSCs driven by covalent bonding interactions, a type of intramolecular force much stronger than the above-mentioned intermolecular forces. A model solution-phase anhydride reaction is used to form covalent bonds between molecules grafted on the surface of gold nanoparticles, resulting in three-dimensional NPSCs. The NPSCs are very stable in different solvents, in dried conditions, and at temperatures as high as 160 °C. In addition to this, the large library of covalent-bond-forming reactions available and the low cost of reactants make the covalent bonding approach highly versatile and economical.

Micelle-Assisted Formation of Nanoparticle Superlattices and Thermally Reversible Symmetry Transitions.

Nanoparticle superlattices (NPSLs) are of great interest as materials with designed emerging properties depending on the lattice symmetry as well as composition. The symmetry transition of NPSLs depending on environmental conditions can be an excellent ground for making new stimuli-responsive functional materials. Here, we report a spherical micelle-assisted method to form exceptionally ordered NPSLs which are inherently sensitive to environmental conditions. Upon mixing functionalized gold nanoparticles (AuNPs) with a nonionic surfactant spherical micellar solution, NPSLs of different symmetries such as NaZn13, MgZn2, and AlB2-type are formed depending on the size ratio between micelles and functionalized AuNPs and composition. The NPSLs formed by the spherical micelle-assisted method show thermally reversible order-order (NaZn13-AlB2) and order-disorder (MgZn2-isotropic) symmetry transitions, which are consistent with the Gibbs free energy calculations for binary hard-sphere model. This approach may open up new possibilities for NPSLs as stimuli-responsive functional materials.

Expression Pattern of Smad4/GATA3 as a Predictor of Survival in Invasive Ductal Carcinoma of the Breast.

BACKGROUND: Smad4 and GATA3 proteins are known prognostic markers in various cancers. Smad4 is a mediator linked to both tumour suppression and progression. GATA3 is a regulator of development and morphogenesis of the mammary gland. We assessed and compared the predictive performance of Smad4 and GATA3 for clinical outcomes in patients with breast cancer. METHODS: The combined expression pattern based on Smad4+/- and GATA3+/- was evaluated by immunostaining using breast cancer tissue microarray, and the relationships between protein expression and clinicopathological variables were analysed. RESULTS: Smad4 expression was only associated with an ill-defined tumour border, whereas GATA3 was associated with several good prognostic factors. On analysis of combined markers, there was a significant difference in the expression of fascin (an important factor for cancer invasiveness) between the Smad4+/GATA3- and Smad4-/GATA3+ groups. Smad4+/GATA3- was correlated with worse clinicopathological parameters, relapse-free survival (RFS), and overall survival (OS), compared to Smad4-/GATA3+. CONCLUSION: Combined markers of Smad4/GATA3 showed a superior performance compared to single markers for predicting RFS and OS in patients with breast cancer.

Nanoparticle Superlattices Driven by Linker-Mediated Covalent Bonding Interaction.

The stability of the nanoparticle superlattice (NPSL) is essential for realizing its broad spectrum of potential applications. Here, we report a linker-mediated covalent bonding interaction method for the synthesis of highly stable NPSLs. Adipic acid is used as a linker molecule which connects two Au NPs functionalized with 6-mercaptohexanol through esterification reactions in the presence of H2SO4. As-prepared NPSLs are mostly fcc Wulff polyhedra with a fairly narrow size distribution and are highly stable in solvents of different polarities and pHs (0-14) as well as in dry conditions and at temperatures as high as 175 °C. The formation of NPSLs involves random homogeneous nucleation simultaneously accompanied by growth, a gradual change of the growth mode from reaction-controlled to diffusion-controlled with time, and the oriented attachments of small crystals. The size of the NPSL can be easily tuned by the concentration of linker molecules and the reaction temperature.

The fabrication of metal silicide nanodot arrays using localized ion implantation.

We propose a process for fabricating nanodot arrays with a pitch size of less than 25 nm. The process consists of localized ion implantation in a metal thin film on a Si wafer using a focused ion beam (FIB), followed by chemical etching. This process utilizes the etching resistivity changes of the ion beam irradiated region that result from metal silicide formation by ion implantation. To control the nanodot diameter, a threshold ion dose model is proposed using the Gaussian distribution of the ion beam intensities. The process is verified by fabricating nanodots with various diameters. The mechanism of etching resistivity is investigated via x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES).

Kinetics of two wave mixing gain for moving grating technique in photorefractive BaTiO3 crystal.

We present analytic expressions for time-dependent space charge field and two wave mixing gain under the external applied field accompanying the grating translation. The variations of complex space charge field are analyzed in a complex plane, and the explicit expressions for the resonance and optimum frequencies (or moving grating velocities), which maximize the magnitude and imaginary part of space charge field, respectively, are also obtained. In addition, two wave mixing experiment was conducted with a grating translation technique without the external applied field in a BaTiO(3) crystal and the transient behaviors of measured gain look like damped harmonic oscillations, showing excellent agreement with the theory for the entire time range.

Orientational photorefractive holograms in porphyrin:Zn-doped nematic liquid crystals.

We investigated the diffraction properties of dynamic holograms recorded in porphyrin:Zn doped nematic liquid crystals (NLCs) under the influence of an applied dc electric field for various conditions of the grating period, the writing beam intensity and the applied electric field. We also derived an analytic expression for diffraction efficiency from NLCs material equations and torque balance equations and compared the experimental results with the theory, revealing excellent agreement.

Synthesis and bidirectional frequency tuning of cantilever-shape nano resonators using a focused ion beam.

The synthesis of cantilever-shape nano resonators and their resonant frequency tunings in both upward and downward directions have been demonstrated using FIB-CVD (focused ion beam-chemical vapor deposition). The in situ experimental observations of mechanical resonances as well as cutting and adding of resonator materials have been accomplished inside the FIB vacuum chamber. Extending the length of the cantilever-shape resonator by 500 nm scale using either the same material or alternating different materials effectively reduced resonant frequency. On the other hand, direct cutting and gradual trimming of the end point of nano resonator increases its resonant frequency. This simple yet versatile synthesis and frequency tuning scheme could be applicable to both constructing micro/nano scale resonators and tuning nanostructures with reduced efforts and enhanced efficiency.

Alteration of stringent response of the Escherichia coli rnpB promoter by mutations in the -35 region.

It is well known that the GC-rich discriminator region between the -10 region and the transcription start site is important for the stringent control of the transcription. However, the discriminator activity is influenced by flanking regions, in particular in conjunction with the promoter -35 and -10 sequences. In this study, we changed the sequence in the -35 region of the rnpB P-1 promoter to see how such changes affect the stringent control. The sequence variation in the -35 region changed the stringent signal. The change to the consensus TTGACA sequence caused the most prominent relieving effect on stringent repression of the rnpB transcription. The spacing between the -35 and -10 regions is also significant because the relieving effect of the TTGACA was offset by the change of the spacing from 17 to 16 bp. The nucleotide just upstream of the -35 region contributes toward generating stringent signals as well.