Nanoscale shuffling in a template-assisted self-assembly of binary colloidal particles

We have fabricated a square lattice array of sub-micrometer fluorescent (red and green) polystyrene particles. The particles were each embedded into small pits fabricated on a silicon substrate by electron beam lithography, through the drying process of an aqueous suspension containing equal amounts of the two species. We indexed 0 and 1 for each red and green particle, respectively, and then obtained a one-dimensional bit sequence by the successive reading of the indices in a predetermined manner. We evaluated the randomness of the bit sequence by using the improved FIPS 140-2 statistical test suite. Consequently, we found that the bit sequences do not have any non-randomness. The particle array was obtained by a very simple process, i.e., the drying of a suspension, but the particle distribution pattern was definitely unpredictable and irreproducible, and the number of possible patterns was tremendously large. The signal--i.e., the color of the particle--does not deteriorate within a practical timescale under various conditions, such as in an electric field, in a magnetic field, in air or water, on a solid matrix, and so on, which means that a small tip with the particle pattern can be installed in miscellaneous object, including electronic products, plastic credit cards, currency bills, and so on. Therefore, this particle array is applicable to a nanoscale identification tag or a one-time pad encryption tip.     

Nanoscale size dependence parameters on lattice thermal conductivity of Wurtzite GaN nanowires

A detailed calculation of lattice thermal conductivity of freestanding Wurtzite GaN nanowires with diameter ranging from 97 to 160 nm in the temperature range 2–300 K, was performed using a modified Callaway model. Both longitudinal and transverse modes are taken into account explicitly in the model. A method is used to calculate the Debye and phonon group velocities for different nanowire diameters from their related melting points. Effect of Gruneisen parameter, surface roughness, and dislocations as structure dependent parameters are successfully used to correlate the calculated values of lattice thermal conductivity to that of the experimentally measured curves. It was observed that Gruneisen parameter will decrease with decreasing nanowire diameters. Scattering of phonons is assumed to be by nanowire boundaries, imperfections, dislocations, electrons, and other phonons via both normal and Umklapp processes. Phonon confinement and size effects as well as the role of dislocation in limiting thermal conductivity are investigated. At high temperatures and for dislocation densities greater than 10¹⁴ m^?2 the lattice thermal conductivity would be limited by dislocation density, but for dislocation densities less than 10¹⁴ m^?2, lattice thermal conductivity would be independent of that.     

Control of surface migration of gold particles on Si nanowires

On the surface of silicon nanowires (SiNWs) synthesized by gold (Au)-catalyzed chemical vapor deposition (CVD), Au particles 5-20 nm in diameter are formed if the growth conditions are within a specific range. We studied the mechanism of Au particle formation by growing SiNWs under different conditions, specifically by dynamically changing the growth parameters during the growth process. We show that insufficient supply of Si source to the Au-Si eutectic on top of the SiNWs enhances the migration of Au atoms on the surface of SiNWs in the form of Au-Si eutectic, which is precipitated on the surface as Au particles during cooling. We also show that using Au-Si eutectic on the surface of SiNWs as a catalyst enables one-step growth of branched SiNWs.     

Quantitative surface acoustic wave detection based on colloidal gold nanoparticles and their bioconjugates

The immobilization scheme of monodispersed gold nanoparticles (10-nm diameter) on piezoelectric substrate surfaces using organosilane molecules as cross-linkers has been developed for lithium niobate (LiNbO3) and silicon oxide (SiO2)/gold-covered lithium tantalate (LiTaO3) of Rayleigh and guided shear horizontal- (guided SH) surface acoustic wave (SAW) sensors. In this study, comparative measurements of gold nanoparticle adsorption kinetics using high-resolution field-emission scanning electron microscopy and SAW sensors allow the frequency responses of SAW sensors to be quantitatively correlated with surface densities of adsorbed nanoparticles. Using this approach, gold nanoparticles are used as the "nanosized mass standards" to scale the mass loading in a wide dynamical range. Rayleigh-SAW and guided SH-SAW sensors are employed here to monitor the surface mass changes on the device surfaces in gas and liquid phases, respectively. The mass sensitivity ( approximately 20 Hz.cm2/ng) of Rayleigh-SAW device (fundamental oscillation frequency of 113.3 MHz in air) is more than 2 orders of magnitude higher than that of conventional 9-MHz quartz crystal microbalance sensors. Furthermore, in situ (aqueous solutions), real-time measurements of adsorption kinetics for both citrate-stabilized gold nanoparticles and DNA-gold nanoparticle conjugates are also demonstrated by guided SH-SAW (fundamental oscillation frequency of 121.3 MHz). By comparing frequency shifts between the adsorption cases of gold nanoparticles and DNA-gold nanoparticle conjugates, the average number of bound oligonucleotides per gold nanoparticle can also be determined. The high mass sensitivity ( approximately 6 Hz.cm2/ng) of guided SH-SAW sensors and successful detection of DNA-gold nanoparticle conjugates paves the way for real-time biosensing in liquids using nanoparticle-enhanced SAW devices.     

Rapid assembly of colloidal monolayer for the synthesis of surface anisotropic particles

A facile and efficient technique for synthesizing rapid and large-scale colloidal monolayer is introduced to obtain surface anisotropic particles. Silica particles grafted with long alkyl chains are rapidly organized into monolayer assemblies by implementing water-film climbing and convective particle assembly on glass slides. Assembled particles are modified into surface-anisotropic particles utilizing physical vapor deposition with a magnetically active material. The magnetic hemisphere enables separation of modified and unmodified surface-anisotropic particles. The proposed methodology can lead to a large-scale production opportunity for surface-anisotropic particles.     

Determining the size and shape dependence of gold nanoparticle uptake into mammalian cells

We investigated the intracellular uptake of different sized and shaped colloidal gold nanoparticles. We showed that kinetics and saturation concentrations are highly dependent upon the physical dimensions of the nanoparticles (e.g., uptake half-life of 14, 50, and 74 nm nanoparticles is 2.10, 1.90, and 2.24 h, respectively). The findings from this study will have implications in the chemical design of nanostructures for biomedical applications (e.g., tuning intracellular delivery rates and amounts by nanoscale dimensions and engineering complex, multifunctional nanostructures for imaging and therapeutics).     

Nanofluidic injection and heterogeneous kinetics of organomercaptan surface displacement reactions on colloidal gold in a microfluidic stream

Colloidal gold is developed as a molecular capture reagent in hybrid nanofluidic-microfluidic devices for mass-limited sample analysis. Two fluorescent organomercaptans are injected through a nanocapillary array membrane and subsequently captured at the surface of 19-nm-diameter colloidal Au nanoparticles. The surface displacement kinetics are monitored via quenching of the organomercaptan fluorescence by the metallic particles coupled to a distance-time conversion based on fluid velocity in the microfluidic channel using the point of mixing as the zero of time. The adsorbate concentration, colloid concentration, and fluid velocity are varied to determine the surface displacement rate constants for these heterogeneous reactions in the microfluidic device. Surface displacement rate constants are approximately 10(4) M(-1) s(-1) for a small organic molecule and for an octapeptide. These values are similar to values determined in macroscale measurements made with a traditional fluorometer and are 1 order of magnitude larger than values reported for adsorption of organomercaptans on planar Au, indicating faster kinetics in the colloid-adsorbate system. These results highlight the utility of colloidal Au nanoparticles as molecular carriers for the sequestration of analytes, allowing the manipulation of mass-limited samples and ultimately the capture and delivery of selected analytes from a microfabricated device to an off-line detector.     

Nanoscale patterning of colloidal quantum dots on transparent and metallic planar surfaces

The patterning of colloidal quantum dots with nanometer resolution is essential for their application in photonics and plasmonics. Several patterning approaches, such as the use of polymer composites, molecular lock-and-key methods, inkjet printing and microcontact printing of quantum dots have been recently developed. Herein, we present a simple method of patterning colloidal quantum dots for photonic nanostructures such as straight lines, rings and dot patterns either on transparent or metallic substrates. Sub-10?nm width of the patterned line could be achieved with a well-defined sidewall profile. Using this method, we demonstrate a surface plasmon launcher from a quantum dot cluster in the visible spectrum.     

Multiple surface plasmon modes for a colloidal solution of nanoporous gold nanorods and their comparison to smooth gold nanorods

The paper represents a novel approach to investigating localized surface plasmon (LSP) resonance modes of nanoporous Au nanorods (NRs) in a solution phase with control over surface morphology. Au NRs, which have distinctive features such as nanopores and ligaments, showed interesting LSP resonance modes depending on the surface morphology and the total length of the structure. Compared with the analogous smooth surface NRs, the LSP modes of nanoporous NRs are red-shifted, which can be interpreted as a longer effective rod length and larger amplitude of plasmon oscillation.     

Nanoscale surface morphology and monomer concentration dependence on impedance of electrocoated 2,2-dimethyl-3,4-propylene-dioxythiophene on carbon fiber microelectrode

Poly(2,2-Dimethyl-3,4-propylenedioxythiophene) (PProDOT-Me2) thin films have been cyclovoltametrically coated onto carbon fiber microelectrode (CFME) as an active functionalized microelectrode. An electrochemical impedance spectroscopic study on the prepared electrodes is reported in this paper which electropolymerization performed under different initial monomer concentrations. The electrochemical impedance data fitted to equivalent circuit model, used to find out numerical values of the proposed components. Effect of the parameters on the capacitive behavior of the (PProDOT-Me2) coated carbon fiber microelectrode and morphology of films obtained by AFM and SEM was discussed. Highly porous coating was obtained at 100 mV/s scan rate and 10 cycles. EDX and ATR-FTIR results indicated the doping of anion of electrolyte due to formation of polaronic and bipolaronic sites. The presence of surface functional groups were determined by ATR-FTIR. Nanoscale conjugated polymer modified carbon fiber microelectrodes exhibited high capacitance of approximately 90 degrees phase angle, and vertical line in Nyquist plot. The capacitive behavior of CFME was increased by this very thin film coating of PProDOT-Me2. The electroactivity of Poly 2,2-Dimethyl-3,4-propylenedioxythiophene on the carbon fiber microelectrode open the possibility of using these coated electrodes for electrochemical microsupercapacitors and biosensor electrodes.     

利用湿化学法对不同粒径硅粉进行表面改性研究

通过湿化学方法,利用硅氢化反应,通过对刻蚀体系、脱氧方式、刻蚀后硅粒子的分离方法等工艺的优化,成功地实现了微米硅、纳米硅及硅量子点的表面烃基改性。傅里叶变换红外光谱及扫描电子显微镜测试结果表明,硅粒子的表面是通过Si—C键的连接方式实现了烃基改性。与改性前相比,改性后的硅粒子具有显著提升的抗氧化性和抗团簇能力,能够在有机溶剂中形成稳定的分散体系。值得一提的是,与未经改性的硅量子点相比,经烃基改性后的硅量子点的荧光发射性能有了大幅提高,有望应用于光电领域。     

Fabrication and self-assembly of the tetrahedron dimpled colloidal particles

Journal of Materials Science - Highly monodisperse, tetrahedral colloidal particles featuring four spherical dimples arranged symmetrically one per face were synthesized via classical seeded...     

Nanoscale structuration and optical properties of thin gold films on textured FTO

In this work, we propose a methodology to synthesize metallic nanoparticles on textured Fluorine Tin Oxide (FTO) surface by laser irradiations of deposited Au films. In particular, the breakup of the Au films into nanoparticles (NPs) is observed as a consequence of the melting and solidification processes induced by laser irradiations. The mean Au NPs size and surface density evolution are analyzed as a function of the laser fluence. Optical characterizations of the glass/FTO/Au NPs multilayer show, in the absorption spectra, plasmonic peaks due to the Au NPs and an improvement of the light absorption efficiency from the sample with larger Au NPs. The simulated trends of the ratio between the scattering and absorption cross section suggest that the absorption efficiency dominates over the scattering efficiency in the spectral range between 200 and 600 nm. The simulation shows that, by varying the NPs radius from about 18 to 24 nm, the radiation-scattered intensity remains symmetric in forward and reverse directions. These results indicate that the surface coverage size distribution of Au NPs is the key parameter to correlate the structural and optical properties of the glass/FTO/Au NPs multilayer. Furthermore, electrical characterizations highlight a reduction in the sheet resistance of the textured FTO due to the presence of the NPs. We compare these results with those obtained for the same systems when standard furnace annealing processes are used to obtain the Au NPs on the textured FTO surface.     

Adsorption of S-S containing proteins on a colloidal silver surface studied by surface-enhanced Raman spectroscopy

We present a Raman and surface-enhanced Raman scattering (SERS) study of the following proteins containing S-S group(s): alpha chymotrypsin (alpha-CHT), insulin, lysozyme, oxytocin (OXT), Streptomyces subtilisin inhibitor (SSI), and trypsin inhibitor (STI). The SERS study is performed in order to understand the adsorption mechanism of the above-mentioned proteins on a colloidal silver surface. The SERS spectra presented here show bands associated mainly with aromatic amino acid vibrations. In addition, two distinct vibrations of the -C-S-S-C- fragment are observed in the Raman and SERS spectra, i.e., nu(SS) and nu(CS). The enhancement of the nu(SS) vibration in the SERS spectra yields evidence that the intact disulfide bridge(s) is (are) located near the silver surface. This finding is supported by the presence of the nu(CS) mode(s). The presence of nus(COO-) and nu(C-COO-) in the SERS spectra in the 1384-1399 cm(-1) and 909-939 cm(-1) regions, respectively, indicate that the negatively charged COO- groups (aspartic and glutamic acids) assist in the binding on the positively charged silver surface. The Raman amide I and III bands observed in the 1621-1633 and 1261-1289 cm(-1) ranges, respectively, indicate that the alpha-helical conformation is favored for binding to the surface over the random coil or beta-sheet conformations. In addition, the presence of the imino group of Trp and/or His indicates that these amino acid residues may also bind to the silver sol.     

Specific surface area,shape, and size of fine carbon filler particles

We have studied the specific surface area, shape, and size of fine particles of isotropic and needle cokes and isotropic graphite. The results demonstrate that, as the average particle size is reduced from 1000 to 1.5 μm, the BET specific surface area of the powders increases from 0.1 to 100 m²/g, exceeding the geometric surface area of the particles by a factor of 40–60. The particle size distributions of the coke and graphite powders produced under identical milling conditions are similar to one another and can be represented by the Rosin-Rammler equation. The anisometry of the powder particles is higher at a stronger microtexture of the starting material and decreases with decreasing particle size.     

Effect of surface modification with carbon-containing groups on the size, properties, and morphology of silica particles

We report the properties of hydrated silica surface-modified with aminopropyl, 3-(2-imidazolin-1-yl)propyl, or 1H,1H,2H,2H-perfluorodecyl. The modifier groups reside on the surface of the silica nanoparticles, as shown by NMR spectroscopy. We examine the effect of the nature and concentration of the modifier on the particle size and specific surface area of silica. Thermal analysis results demonstrate that the modified materials are stable up to 430°C.     

The effect of arginine on gold nanoparticles in colloidal solutions and in thin films

Gold nanoparticles were prepared in aqueous colloidal solutions and their interaction with L-arginine solutions at different concentrations was investigated by UV-vis spectroscopy, transmission electron microscopy (TEM) and atomic force microscopy (AFM). The shift towards red of the absorption maximum of gold nanoparticles with increasing L-arginine concentration and in time, and the apparition of a new large band at higher wavelength evidence the formation of assemblies of gold nanoparticles, mediated by the amino acid. TEM images present the progress in the building process of supermolecular structures. Further, the AFM images show the self assemblies of gold nanoparticles capped with L-arginine well ordered in large domains on silanized glass. As a model for the process, we suggest that the positively charged guanidinium group of L-arginine is anchored on the negative citrate capped gold nanoparticles, while the other two functionalities of L-arginine are involved in the bonding between gold nanoparticles. The ability of arginine to specifically bind gold nanoparticles could lead to an increased ability of proteins, containing arginine, to specifically bind to nanogold. Then, they bind other target proteins or different ligands underlying numerous biological and medical applications that range from nanoscale biosensors, cell-cell communications to targeted delivery of drugs to cancer cells.