Sonochemical deposition of Au nanoparticles on titania and the significant decrease in the melting point of gold

In this article, sub-micron size particles of titania were coated by a nanosized gold particles with the aid of power ultrasound. We could achieve a uniform coating of gold nanoparticles on a titania surface with a maximum gold loading of 10 wt%. In addition, we report on the experimental evidence for a significant decrease in the melting point of gold nanoparticles (<2 nm) by approximately 850 degrees C from that of the bulk material.     

Enhancing sensitivity and selectivity of long-period grating sensors using structure-switching aptamers bound to gold-doped macroporous silica coatings

High surface area, sol-gel derived macroporous silica films doped with gold nanoparticles (AuNP) are used as a platform for high-density affinity-based immobilization of functional structure-switching DNA aptamer molecules onto Michelson interferometer long-period grating (LPG) fiber sensors, allowing for label-free detection of small molecular weight analytes such as adenosine triphosphate (ATP). The high surface area afforded by the sol-gel derived material allowed high loading of DNA aptamers, while the inclusion of gold nanoparticles within the silica film provided a high refractive index (RI) overlay, which is required to enhance the sensitivity of the LPG sensor according to our numerical simulations. By using a structure-switching aptamer construct that could release an oligonucleotide upon binding of ATP, the effective change in RI was both enhanced and inverted (i.e., binding of ATP caused a net reduction in molecular weight and refractive index), resulting in a system that prevented signals originating from nonspecific binding. This is the first report on the coupling of aptamers to LPG fiber sensors and the first use of high RI AuNP/silica films as supports to immobilize biomolecules onto the LPG sensor surface. The dual functionality of such films to both improve binding density and LPG sensor cladding refractive index results in a substantial enhancement in the sensitivity of such sensors for small molecule detection.     

Selective Patterning of Gold Surfaces by Core/Shell,Semisoft Hybrid Nanoparticles

The generation of patterned surfaces with well‐defined nano‐ and microdomains is demonstrated by attaching core/shell, semisoft nanoparticles with narrow size distribution to microdomains of a gold‐coated silicon wafer. Near monodisperse nanoparticles are prepared using reversible addition‐fragmentation chain transfer (RAFT) polymerization, initiated from a silica surface, to prepare a polystyrene shell around a silica core. The particles are then used as‐prepared, or after aminolysis of the terminal thiocarbonyl group of the polystyrene shell, to give thiol‐terminated nanoparticles. When gold‐coated silicon wafers are immersed into very dilute suspensions of these particles (as low as 0.004 wt%), both types of particles are shown to adhere to the gold domains. The thiolated particles adhere selectively to the gold microdomains, allowing for microdomain patterning, while particles that contain the trithiocarbonate functionality lead to a much more even coverage of the gold surface with fewer particle aggregations.     

Fabrication of Janus particles via a “photografting-from” method and gold photoreduction

Faster and simpler methods for the fabrication of Janus particles are of tremendous importance for a real implementation of these particles. By combining thiol-modified silica particles (SMPs) with the use of UV light, it is possible to rapidly fabricate Janus particles coated with polymer brushes and gold nanoparticles via photochemical emulsion-assisted route. From the silica particle surface, polymeric brushes of polyethylene(glycol), PEG, were grafted via a photografting-from method on one hemisphere by using the thiol groups as photoinitiator of the polymerization. The other hemisphere was coated with gold nanoparticles (AuNPs) generated in situ via photoreduction of chloroauric acid promoted by Norrish type I photoinitiator. PEG/AuNPs@SMPs coated with Au nanoparticles with average diameter of 12.7 or 22.5 nm were obtained by playing on the mass ratio between thiol-modified silica particles and gold precursor. The Janus PEG/AuNPs@SMPs were fully characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and UV–Vis spectroscopy. This strategy merges the advantages of emulsion-based selective masking and UV-induced reactions, and it is proved to be a feasible and fast route (reactions are completed in dozens of minutes) for Janus particles fabrication.     

Gas-phase production of gold-decorated silica nanoparticles

Gold-decorated silica nanoparticles were synthesized in a two-step process in which silica nanoparticles were produced by chemical vapor synthesis using tetraethylorthosilicate (TEOS) and subsequently decorated using two different gas-phase evaporative techniques. Both evaporative processes resulted in gold decoration of the silica particles. This study compares the mechanisms of particle decoration for a production method in which the gas and particles remain cool to a method in which the entire aerosol is heated. Results of transmission electron microscopy and visible spectroscopy studies indicate that both methods produce particles with similar morphologies and nearly identical absorption spectra, with peak absorption at 500-550 nm. A study of the thermal stability of the particles using heated-TEM indicates that the gold decoration on the particle surface remains stable at temperatures below 900?°C, above which the gold decoration begins to both evaporate and coalesce.     

Paramagnetic silica-coated gold nanoparticles

Water soluble gold nanoparticles, obtained by the reduction of the gold (III) chloride with sodium borohydride in the presence of citric acid or thioctic acid, were covered with a paramagnetic silica layer using the Stober method, yielding a hybrid metallic-inorganic nanomaterial (gold nanoparticles, with an average size of 5 nm, embedded into silica nanoparticles, with an average size of 100 nm). The paramagnetic silica layer was formed by copolymerization of a paramagnetic silica precursor (derived from 3-aminopropyltrimethoxysilane) with tetramethyorthosilicate. The paramagnetic silica precursor was obtained by coupling 3-aminopropyltrimethoxysilane with 3-carboxy-proxyl free radical. TEM pictures show that each silica nanoparticle of about 100 nm in size embedded about 10 gold nanoparticles. These hybrid nanoparticles are quite stable and exhibit the expected paramagnetic characteristics, as seen by electron paramagnetic resonance. The accessibility of methanol through the silica layer was also studied. Depending on the capping ligands of the gold nanoparticles (citric or thioctic acid), different silica networks are formed, as seen by the mobility of the spin-label inside the silica layer. The EPR spectra showed that the paramagnetic silica layer is very robust and the mobility of the spin-probe inside the silica layer is very little affected by methanol. However, if spin-labeled thioctic acid protected gold nanoparticles were used in the material synthesis, the mobility of the spins attached to the gold surface is quite high in the presence of methanol, while the spins embedded into the silica layer remains immobilized.     

Kinetic studies on water-soluble gold nanoparticles coordinated to poly(vinylpyrrolidone): isotropic to anisotropic transformation and morphology

The growth kinetics, isotropic-to-anisotropic transformation, structural properties and surface morphology of polyvinylpyrrolidone (PVP)-coordinated gold nanoparticles are reported in this work. The reduction of gold ions, kinetics, and growth mechanism of gold nanoparticles, and the coordination between PVP and gold are explored for the first time in this single report. The layer-by-layer growth mechanism (adsorption of gold ions to the nuclei and their subsequent reduction) was observed in the growth of isotropic nanoparticles during the initial stage of the reaction, whereas the Ostwald ripening mechanism (growth of larger particles at the expense of smaller particles) was observed in the growth of the anisotropic nanoparticles in the later stage of the reaction. The surface plasmon resonance band for the anisotropic nanoparticles (average size for a typical sample was ca. 9 nm) was blue-shifted (20 nm) toward that of the isotropic nanoparticles (whose average size is much smaller than that of the anisotropic nanoparticles). The increased effective electron density on the surface of anisotropic particles was the cause of this blue shift. The resultant gold colloids were very stable because the PVP molecules were coordinated through both the C–N and C=O groups, instead of the C=O group alone. The positions of the surface plasmon band and morphology of the gold products were strongly dependent on the amount of PVP.     

Heparin conjugated silica nanoparticle synthesis

We report on a facile method towards a synthesis of novel hybrid heparin silica nanoparticles involving a modification of the Stober method. Tetrapropyl orthosilicate (TPOS) was used instead of the traditional TEOS or TMOS; by this way we could overcome the solubility problems of heparin in ethanol and exploit the good solubility of heparin in proper isopropanol–water mixtures. Aminopropyl triethoxysilane (APTS) was also used to have a good link of heparin to silica particles. SEM, DLS, FTIR and NMR proved that we did find conditions in which heparin conjugated silica particles were produced.Thermogravimetry allowed to evaluate the heparin/silica weight ratio to be 0.61. The efficiency of heparin binding to the particles was appreciated to be 35 wt.%.     

Continuous laser irradiation under ambient conditions: A simple way for the space-selective growth of gold nanoparticles inside a silica monolith

Thanks to the potential and various applications of metal-dielectric nanocomposites, their syntheses constitute an interesting subject in material research. In this work, we demonstrate the achievement of gold nanocrystals growth through a visible and continuous laser irradiation. The in situ and direct space-selective generation of metallic nanoparticles is localized under the surface within transparent silica monoliths. For that purpose, the porous silica monoliths are prepared using a sol-gel route and post-doped with gold precursors before the irradiation. The presence of Au nanoparticles inside the irradiated areas was evidenced using absorption spectroscopy, X-ray diffraction analysis and transmission electron microscopy. The comparison between the results obtained after a laser irradiation and by a simple heat-treatment reveals that the local precipitation of gold nanoparticles by continuous photo-irradiation occurs following a photo-thermal activated mechanism.     

Quantifying ligand adsorption to nanoparticles using tandem differential mobility mass analysis

Although electrospray-differential mobility analyzers (ES-DMA) have been previously employed to characterize ligand binding to nanoparticles, absolute quantification of surface coverage can be inaccurate at times because of ligand conformational effects. In this Letter, we report a quantitative technique by in-flight coupling of a particle mass analyzer (APM) with ES-DMA, thus enabling a direct quantitative analysis of mass independent of particle size, material, morphology and conformation. We demonstrate the utility of ES-DMA-APM by studying two model complex systems (gold nanoparticle-bovine serum albumin and polystyrene bead-antibody) as a function of concentration and pH. Our results obtained with ES-DMA-APM are in excellent agreement with prior work. We anticipate that this will enhance the capabilities of online quantitative characterization of ligand binding to nanoparticles.     

Radical scavenger for the stabilization of gold nanoparticles

In this contribution, we report the photo-catalytic synthesis of gold nanoparticles using poly(vinyl alcohol) as a radical surfactant stabilizer. Small Au nanoparticles were prepared depending on the concentration of the stabilizer. Both particle size and surface plasmon band are dependent on the concentration of poly(vinyl alcohol) and irradiation time. Transmission electron microscopic image and dynamic light scattering measurement shows that particles are spherical and monodispersed, respectively. This approach provides a simple route to fabricate gold nanoparticles that hold much promise for use in catalysis, chemical sensing, and biolabeling.     

Increasing surface area of silica nanoparticles with a rough surface

The silica nanoparticles with a rough surface were developed using a silane precursor in a reverse microemulsion followed by a drying treatment. The surface roughness of the nanoparticles was adjustable by changing the amount of the precursor. Within a certain range, the roughness increased as the amount of the silane precursor increased. The rough surface provided a larger surface area than the smooth one. The produced nanoparticles were characterized using the transmission electron microscopy, ultraviolet-visible spectroscopy, energy-dispersive X-ray elemental analysis, and Brunauer-Emmet-Teller analysis technique. Additionally, the amount of surface functional amino groups on the nanoparticles was detected using the traditional acid-base titration and the dissociation constant of this functional group was calculated. On the basis of the experimental results, the mechanism of the formation of the rough surface was proposed. Finally, the produced silica nanoparticles were utilized as a carrier for the chemical binding of a near-infrared dye molecule and the adsorption of the gold nanoparticles. The results demonstrated that the rough surface provide the silica nanoparticles with a high capacity of surface chemical and supramolecular reactions.     

Significantly improved trapping lifetime of nanoparticles in an optical trap using feedback control

We demonstrate an increase in trapping lifetime for optically trapped nanoparticles by more than an order of magnitude using feedback control, with no corresponding increase in beam power. Langevin dynamics simulations were used to design the control law, and this technique was then demonstrated experimentally using 100 nm gold particles and 350 nm silica particles. No particle escapes were detected with the controller on, leading to lower limits on the increase in lifetime for 100 nm gold particles of 26 times (at constant average beam power) and 22 times for 350 nm silica particles (with average beam power reduced by one-third). The approach described here can be combined with other techniques, such as counter propagating beams or higher-order optical modes, to trap the smallest nanoparticles and can be used to reduce optical heating of particles that are susceptible to photodamage, such as biological systems.     

Corona Generation and Deposition of Metal Nanoparticles on Conductive Surfaces and Their Effects on the Substrate Surface Texture and Chemistry

A corona discharge ion bombardment technique was used successfully to generate gold particles of submicron diameters. In a negative corona discharge, the glow region contains electrons, negative ions, and positive ions. Positive ions collided with the negative corona tip electrode, causing it to sputter and emit fine particles of the electrode material. These nanoparticles were deposited on grounded metal substrates or thin mica sheets supported by grounded metal substrates. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to study the size distribution and deposition pattern of the metal nanoparticles. The diameter of these nanoparticles was dependent upon the material of the electrode and ranged from 20 to 450 nm for gold and from 15 to 240 nm for tungsten. The nanoparticles were deposited on aluminum, mica, and carbon steel test panels for different amounts of time. The electrochemical response of the carbon steel panels exposed to aerated salt solution was measured by direct current (DC) polarization technique before and after the gold nanoparticles were deposited. This technique was employed to determine the changes in the surface chemistry because of the presence of gold nanoparticles, and it proved to be a sensible method for detecting the presence of fine layers of nanoparticles on the metallic substrate. The presence of the gold nanoparticles increased the electrochemical potential E_corr from -0.640 V to -0.211 V, compared with the value for a noncorrosive surface, like that of pure gold, which is 0 V.     

Facile route for preparation of silica-silver heterogeneous nanocomposite particles using alcohol reduction method

Silica-silver heterogeneous nanocomposite particles were successfully prepared by facile route including alcohol reduction method. Thiol groups were employed as a chemical protocol to make a binding between silver nanoparticle and silica surface. After the reaction for 10 min, a large number of quasi-spherical silver nanoparticles with an average size of 6.9 nm in diameter were homogeneously formed on the surface of silica particles. The immobilized silver nanoparticles grew to large ones with an average size of 10.6 nm in diameter after additional reaction for 2 h. The resulting nanocomposite particles were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), UV-vis spectrophotometer, and X-ray diffraction (XRD) analysis.     

Langmuir-Blodgett films of gold/silica core/shell nanorods

We report the preparation of Langmuir- and Langmuir-Blodgett films of mesoporous silica coated gold nanorods. The silica coating on the gold nanorods was found to prevent the aggregation of the plasmonic particles trapped at the air/water interface. Due to the small aspect ratio of the gold core and the presence of the silica shell, the orientational alignment of the nanorods in the Langmuir-Blodgett film is hindered. After particle deposition, no plasmon coupling was observed, which enables the design of the resulting film's optical property at the particle level. By using mesoporous silica as the shell material, the accessibility of the metal core's surface is preserved. Organic dye (Rhodamine 6G) was found to be able to penetrate into the mesoporous shell of the gold nanorods, resulting in a red shift of the longitudinal plasmon mode.     

Biomimetic approach to the formation of gold nanoparticle/silica core/shell structures and subsequent bioconjugation

The encapsulation of individual nanoparticles has gained great attention as a method for both stabilizing nanoparticles and tailoring their surface properties. In particular, the encapsulation of nanoparticles with silica shells is advantageous for bioconjugation and applications to (nano)biotechnology. Herein we report a method for constructing gold nanoparticle (AuNP)/silica core/shell hybrid structures by biomimetic silicification of silicic acids. The procedure consists of surface-initiated, atom transfer radical polymerization of 2-(dimethylamino)ethyl methacrylate (DMAEMA) from AuNPs and biomimetic polycondensation of silicic acids by using poly(DMAEMA) as a synthetic counterpart for silaffins that are found in diatoms. The resulting AuNP/silica hybrids were characterized by Fourier transform infrared spectroscopy, energy dispersive x-ray spectroscopy, UV-vis spectroscopy and transmission electron microscopy. In addition, the immobilization of biological ligands onto the hybrids was investigated for potential applications to biotechnology. As a model ligand, biotin was attached onto the AuNP/silica hybrids through substitution reaction and Michael addition reaction, and the attachment was confirmed by fluorescence microscopy after complexation with fluorescein-conjugated streptavidin.     

Rayleigh like scattering from silica–titania core-shell particles and their application in protection against harmful ultraviolet rays

In this article we report experimental and theoretical results of angle-dependent laser light scattering of nano titanium dioxide nucleated on silica particles. It was observed that the experimental scattering profile from nano-titania coated silica (TCS) particle resembles that of a Rayleigh scattering. It can be inferred from the light scattering profile that nucleating fine particles onto a surface of a bigger particle (core), the resulting scattering profile is dominated by the smaller particles. Thin film transmittance measurement of TCS particles also supports this claim. The theoretical scattering predictions do not match with the experimental findings and the reasons for the discrepancies are addressed. This Rayleigh-like scattering property of TCS particles can be used in cosmetic formulations as a replacement for nanoparticles to provide protection from harmful ultraviolet rays. This study helps to provide insights into these systems for their potential usage in cosmetics.     

Biosynthesis of controllable size and shape gold nanoparticles by black seed (Nigella sativa) extract

We report on the use of black seed (Nigella sativa) extract, previously not exploited, in synthesis of gold nanoparticles. On treating aqueous chloroauric acid solution with black seed extract, the antioxidant activities critical roles of the various phytochemicals is observed leading to the formation of crystalline and poly shaped gold nanoparticles. In this research work, we developed a rapid and non-toxic method for the preparation of biocompatible gold nanoparticles by two different synthetic routes: microwave irradiation and thermo-induced procedures. The nanoparticles were characterized and investigated by ultraviolet-visible (UV-Vis) spectrophotometry, transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, and X-ray diffraction (XRD).The size and shape of the nanoparticles were found to be very sensitive to the quantity of the extract. As the amount of extract is increased, the stronger the interaction between the extract biomolecules and nascent nanoparticles, thus the yield of nanoparticles increased as shown by surface plasmon resonance bands in the UV-vis-NIR spectra. The reaction temperature has a significant role in production of gold nanoparticles with different shapes. The XRD studies reflect an interesting feature indicates that gold nanocrystals are highly anisotropic in nature, mainly triangular and hexagonal shapes, and that the particles are (111) oriented. The observed characteristics suggest the application of the biocompatible gold nanoparticles to future in vivo imaging and therapy.     

Metal nanoshell assembly on a virus bioscaffold

Chilo iridescent virus is demonstrated as a useful core substrate in the fabrication of metallodielectric, plasmonic nanostructures. A gold shell is assembled around the wild-type viral core by attaching small, 2-5-nm gold nanoparticles to the virus surface by means of the chemical functionality found inherently on the surface of the proteinaceous viral capsid. The density of these nucleation sites was maximized by reducing the repulsive forces between the gold particles through electrolyte addition. These gold nanoparticles then act as nucleation sites for the electroless deposition of gold ions from solution around the biotemplate. The optical extinction spectra of the metalloviral complex is in quantitative agreement with Mie scattering theory. Overall, the utilization of a native virus and the inherent chemical functionality of the capsid afford the ability to grow and harvest biotemplates for metallodielectric nanoshells in large quantities, potentially providing cores with a narrower size distribution and smaller diameters (below 80 nm) than for currently used silica.