Electrostatic-assembly metallized nanoparticles network by DNA template

Eighteen-nanometer gold and 3.5-nm silver colloidal particles closely packed by cetyltrimethylammonium bromide (CTAB) to form its positively charged shell. The DNA network was formed on a mica substrate firstly. Later, CTAB-capped gold or silver colloidal solutions were cast onto DNA network surface. It was found that the gold or silver nanoparticles metallized networks were formed owing to the electrostatic-driven template assembling of positive charge of CTAB-capped gold and silver particles on the negatively charged phosphate groups of DNA molecules by the characterizations of AFM, XPS and UV-vis. This method may provide a novel and simple way to studying nanoparticles assembly conjugating DNA molecules and offer some potential promising applications in nanocatalysis, nanoelectronics, and nanosensor on the basis of the fabricated metal nanoparticles network.     

Shape-directing role of cetyltrimethylammonium bromide in the preparation of silver nanoparticles

We report a simple chemical reduction method for the synthesis of different colored silver nanoparticles, AgNP, using tyrosine as a reducing agent. Effects of cetyltrimethylammonium bromide, CTAB, and tyrosine concentrations are analyzed by UV-visible measurements and scanning electron microscopy (SEM) to evaluate the mode of AgNP aggregation. The position and shape of the surface resonance plasmon absorption bands strongly depend on the reaction conditions, i.e., [CTAB], [tyrosine], and reaction time. Sub-, post-, and dilution-micellar effects are accountable for the fast and slow nucleation and growth processes. Spectrophotometric measurement also shows that the average size and the polydispersity of AgNP increase with [CTAB] in the solution. CTAB acted as a shape-directing agent.     

Surfactant-assisted synthesis and characterization of stable silver bromide nanoparticles in aqueous media

Colloidal dispersions of silver bromide (AgBr) in aqueous surfactant medium have been prepared using a surfactant-assisted synthesis approach with hexadecyltrimethylammonium bromide (CTAB). The surfactant acts both as source of bromide ion as well as the stabilizing agent. Upon progressive addition of silver nitrate to aqueous CTAB solution, stable AgBr dispersions were obtained. Formation of surfactant cation (CTA(+)) stabilized AgBr was confirmed by way of XRD, FTIR and NMR studies. Thermal behavior of the isolated nanoparticles was investigated by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA), where the occurrence of phase transition in the surfactant-stabilized nanoparticles was observed. Kinetics of the particle growth was investigated by dynamic light scattering measurements, which predicted the formation of surfactant bilayered structures associated with the nanoparticles of AgBr. Band gap of the nanoparticles was determined by suitably analyzing the UV-visible spectral data, which concluded that the particles behaved like insulators. Morphology of the particles, studied by TEM measurements, was found to be spherical. Finally, enthalpy of formation of surfactant-stabilized AgBr, determined calorimetrically, was found to be dependent on the concentration of the precursors.     

Photochemical reactions of ketones to synthesize gold nanorods

Photochemical synthesis of gold nanorods (NRs) in a micellar solution of hexadecyltrimethylammonium bromide (CTAB) was triggered by photoreactions of ketones. Photoexcitation of gold ions and silver bromide clusters ((AgBr)n) in the absence of ketones did not produce NRs. The initial products of the photoirradiation were probably ketyl radicals, which then initiated reactions to form NRs. NRs formed in darkness, if the reaction solutions were irradiated by UV light for a few minutes, thus indicating that the photochemical products catalyzed NR-formation.     

Short gold nanorod growth revisited: the critical role of the bromide counterion

A one-step, surfactant-assisted, seed-mediated method has been utilized for the growth of short gold nanorods with reasonable yield by modifying an established synthesis protocol. Among the various parameters that influence nanorod growth, the impact of the bromide counterion has been closely scrutinized. During this study it has been shown that, irrespective of its origin, the bromide counterion [cetyltrimethylammonium bromide (CTAB) or NaBr] plays a crucial role in the formation of nanorods in the sense that there is a critical [Br(-)]/[Au(3+)] ratio (around 200) to achieve nanorods with a maximum aspect ratio. Beyond this value, bromide can be considered as a poisoning agent unless shorter nanorods are required. The use of AgNO(3) helps in symmetry breaking for gold nanorod growth, whereas the bromide counterion controls the growth kinetics by selective adsorption on the facets of the growth direction. Thus, a proper balance between bromide ions and gold cations is also one of the necessary parameters for controlling the size of the gold nanorods; this has been discussed thoroughly. The results have been discussed based on their absorption spectra and finally shape evolution has been confirmed by TEM. Due to their efficient absorption in the near-IR region, these short nanorods were used in photothermal imaging of living COS-7 cells with improved signal-to-background ratios.     

Silver/silver bromide/polypyrrole nanoparticles obtained by microemulsion photopolymerization in the presence of a cationic surfactant

Conductive silver/silver bromide/polypyrrole nanoparticles were obtained by photopolymerization in o/w microemulsions of pyrrole monomer in the presence of silver nitrate as electron acceptor and dopant under UV light irradiation. The microemulsions were prepared using cetyltrimethylammonium bromide (CTAB) as cationic surfactant. The particles were analyzed by scanning electron microscopy (SEM), UV/Vis, Fourier transform infrared spectroscopy, cyclic voltammetry, and X-ray diffraction (XRD). It was observed from SEM analysis that spherical particles can be obtained by this procedure with relatively narrow particles sizes distributions and average particle diameters of the silver cores (Dp) between 39 and 46 nm, which decreases as the surfactant concentration is increased. The conductivities of the resulting materials were between 0.12 and 0.40 S/m. Formation of cores of Ag and AgBr were observed from the XRD analysis, which was ascribed to the reduction of Ag⁺ to Ag⁰ and to reaction of Ag⁺ with the counterion of CTAB surfactant, respectively.     

Transfer of biosynthesized gold nanoparticles from water into an ionic liquid using alkyltrimethyl ammonium bromide: an anion-exchange process

Biosynthesized gold nanoparticles (GNPs) were transferred from water to a hydrophobic ionic liquid (IL), [Bmim]PF(6), with the assistance of alkyl trimethyl ammonium bromide. The phase transfer mechanism was illustrated through the exemplification of cetyltrimethyl ammonium bromide (CTAB). Interaction between GNPs and CTAB was demonstrated through zeta potential analysis. Moreover, an anion-exchange process was discovered between CTAB and IL. During the process, the hydrophobic CTAPF(6) formed in situ on the GNPs led to the hydrophobization and thus phase transfer of the GNPs. The phase transfer efficiency was found to be size-dependent.     

Studies of electrochemical quantized capacitance charging of surface ensembles of silver nanoparticles

CTAB-stabilized silver nanoparticles were synthesized by NaBH₄ reduction. The as-prepared nanoparticles can be self-assembled on 3-mercaptopropionic acid (MPA) modified gold electrode, which was supported strongly by XPS measurements. Exceptional long-term stability of the as-prepared colloidal silver aqueous solution and the desorption of silver nanoparticle ensemble on MPA after alcohol rinsing proved that these CTAB molecules adsorbed on silver core formed interdigitated bilayer structure. DPV and differential capacitance measurements were performed to characterize the as-prepared silver nanoparticle ensemble, and the interesting quantized capacitance charging behaviors were observed.     

Short aspect ratio gold nanorods prepared using gamma radiation in the presence of cetyltrimethyl ammonium bromide (CTAB) as a directing agent

The synthesis of short aspect ratio gold nanorods using gamma radiation method by incorporating cetyltrimethyl ammonium bromide (CTAB) as a directing agent is reported in this communication. The radiolysis of Au⁺, in the presence of 2.5 nm Au seeds and 0.1 mol dm^?3 isopropanol, results in the formation of Au spheres as evident from surface plasmon resonance band at 527 nm. However, by carrying out radiolysis at lower radiation dose rate, short aspect gold nanorods having surface plasmon bands at 513 and 670 nm have been prepared. The formation of rods at low radiation dose rate was observed to be governed by the kinetics of particle growth. The TEM of as-synthesized nanoparticles confirmed the formation of uniform sized nanorods having an aspect of 2.4.     

基于离心技术的金纳米粒子表面清洁方法和机理研究

本文发展了一种基于离心技术的清洗金纳米八面体表面十六烷基三甲基溴化铵(CTAB)吸附物的有效方法.选择合适的离心转速和离心次数,可以驱除金纳米八面体表面的CTAB分子.通过热失重分析、表面增强拉曼光谱和傅里叶红外光谱表征可以推测,金纳米八面体经合适的离心清洗后,表面残留的少量CTAB分子通过疏水作用由烷基长链与金表面形成(亚)单层吸附,同时,与金表面有强相互作用的溴离子发生脱附.溶剂水对CTAB的稀释在离心清洗金纳米八面体表面的过程中发挥着重要作用.金纳米粒子在离心场中的高速运动导致粒子周围双电层发生极化,极化双电层内产生的局部液流引起双电层内物质交换从而也影响了金纳米八面体表面的清洗效果.金纳米八面体在硫酸溶液和碱性硝酸铅溶液中的电化学研究表明,经过离心清洗的金纳米八面体可以直接应用于单晶电化学研究.     

Defining rules for the shape evolution of gold nanoparticles

The roles of silver ions and halides (chloride, bromide, and iodide) in the seed-mediated synthesis of gold nanostructures have been investigated, and their influence on the growth of 10 classes of nanoparticles that differ in shape has been determined. We systematically studied the effects that each chemical component has on the particle shape, on the rate of particle formation, and on the chemical composition of the particle surface. We demonstrate that halides can be used to (1) adjust the reduction potential of the gold ion species in solution and (2) passivate the gold nanoparticle surface, both of which control the reaction kinetics and thus enable the selective synthesis of a series of different particle shapes. We also show that silver ions can be used as an underpotential deposition agent to access a different set of particle shapes by controlling growth of the resulting gold nanoparticles through surface passivation (more so than kinetic effects). Importantly, we show that the density of silver coverage can be controlled by the amount and type of halide present in solution. This behavior arises from the decreasing stability of the underpotentially deposited silver layer in the presence of larger halides due to the relative strengths of the Ag(+)/Ag(0)-halide and Au(+)/Au(0)-halide interactions, as well as the passivation effects of the halides on the gold particle surface. We summarize this work by proposing a set of design considerations for controlling the growth and final shape of gold nanoparticles prepared by seed-mediated syntheses through the judicious use of halides and silver ions.     

Light scattering investigations on mercury ion induced amalgamation of gold nanoparticles in aqueous medium

With the aids of SEM,XPS measurements,localized plasmon resonance light scattering(PRLS) spectrometry and light scattering imaging,investigations on the amalgamation process of both cetyltrimethylammonium bromide(CTAB) and citrate-coated gold nanoparticles(AuNPs) in the presence of Hg2+ showed that the Au-Hg amalgam process of gold nanoparticles is surface coating dependent in aqueous medium,and the scattering light color change of AuNPs under a dark-field microscope is blue-shifted from red-orange into yellow-orange or even yellow.The former one involves the reduction of Hg2+ to Hg0 species and adsorption of Hg0 on the surfaces of AuNPs,while the later one indicates the shape-evolution of AuNPs.     

Combinatorial electrochemistry using metal nanoparticles: from proof-of-concept to practical realisation for bromide detection

Principles and practical application of combinatorial electrochemistry in search for new electroactive materials in electroanalysis have been explored. Nanoparticles of three different metals: silver, gold and palladium have been independently synthesized on the glassy carbon spherical powder surface by electroless deposition process and characterized using both spectroscopic and electrochemical techniques. These three materials were then combined together onto basal plane pyrolytic graphite electrode surface and the application of the combinatorial approach to find the electrode material for bromide detection as model target analyte was demonstrated. The component electroactive for bromide detection was next identified and it was found that silver nanoparticles were the active ones. A composite electrode based on silver nanoparticle modified glassy carbon powder and epoxy resin was then fabricated and it was found to allow accurate determination of bromide. The electroactivity for the bromide determination of the composite electrode was compared with that of a bulk silver electrode and it was shown that the composite electrode is very efficient with a comparable electroactivity with only a portion of precious metals being used for its construction.     

Synthesis of ordered spiral and ring-like polypyrrole nanowires in cetyltrimethylammounium bromide crystalline suspension

Spiral dislocation morphology on the surface of cetyltrimethylammounium bromide (CTAB) crystallites has been discovered for the first time. By addition of ammonium peroxydisulfate into CTAB crystalline suspension, a drastic change in the morphology of result crystallites is observed from spiral to two dimensional (2D) islands. The spiral and 2D-island structures of these crystallites could be use as the templates for the synthesis of spiral and ring-like polypyrrole (PPy) nanowires, respectively, via direct chemical oxidative polymerization of pyrrole due to the oxidation reaction occurring preferentially at the steps of these crystallites. The mechanism of adsorption of pyrrole oligomers on the steps of these crystallites is proposed for the growth of PPy spiral and ring-like nanowires.     

Immobilization of gold nanorods onto acid-terminated self-assembled monolayers via electrostatic interactions

We report the immobilization of gold nanorods onto self-assembled monolayers (SAMs) of 16-mercaptohexadecanoic acid (16-MHA). The simple two step protocol involves formation of a SAM of 16-MHA molecules onto gold-coated glass slides and subsequent immersion of these slides into the gold nanorod solution. The nanorods, formed by a seed-mediated, surfactant-assisted synthesis protocol, are stabilized in solution due to surface modification by the surfactant cetyltrimethylammonium bromide (CTAB). Attractive electrostatic interactions between the carboxylic acid group on the SAM and the positively charged CTAB molecules are likely responsible for the nanorod immobilization. UV-vis spectroscopy has been used to follow the kinetics of the nanorod immobilization. The nature of interaction between the gold nanorods and the 16-MHA SAM has been probed by Fourier transform infrared spectroscopy (FTIR). The surface morphology of the immobilized rods is studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements. SEM was also used to determine the density of the immobilized nanorods as a function of the pH of immobilization. Control over the surface coverage of the immobilized gold nanorods has been demonstrated by simple pH variation. Such well-dispersed immobilized gold nanorods with control over the surface coverage could be interesting substrates for applications such as surface-enhanced Raman spectroscopy (SERS).     

Surfactant displacement of human serum albumin adsorbed on loosely packed self-assembled monolayers: cetyltrimethylammonium bromide versus sodium dodecyl sulfate

The surfactants sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) displace human serum albumin (HSA) from loosely packed self-assembled monolayers (SAM) of hydrophobic alkyl chains by different means. Removal of HSA is of interest because previous work has suggested that the adsorption of HSA to such loosely packed SAMs may be sufficiently tenacious to offer opportunities for surface passivation. While HSA remains on the surface after exposure to SDS and rinsing, no protein remains after exposure to CTAB and rinsing. X-ray reflectivity and X-ray photoelectron spectroscopy measurements indicate that CTAB molecules remain interdigitated in the loosely packed SAM after rinsing, suggesting that CTAB is more effective in removing the HSA because it interacts more strongly with the SAM.     

Photothermal reshaping of gold nanorods depends on the passivating layers of the nanorod surfaces

Photothermal reshaping of gold nanorods was triggered by pulsed-laser irradiation. The efficiency of the reshaping was strongly dependent on the surface conditions of the gold nanorods. When the gold nanorods were dispersed in concentrated hexadecyltrimethylammonium bromide (CTAB), the gold nanorods were efficiently transformed into a phi-shape. By comparison when poly(styrene sulfonate), poly(vinylpyrrolidone), poly(ethylene glycol), or phosphatidylcholine layers were used, the CTAB layers were found to be a better thermal insulator that helped to enhance the photothermal reshaping of the gold nanorods.     

Efficiently removing cetyl trimethyl ammonium bromide from wastewater by graphene oxide

Cetyl trimethyl ammonium bromide (CTAB) containing wastewater from dressing plant may pose a detrimental threaten to mineral beneficiation and environment. The adsorption of CTAB in aqueous solutions by graphene oxide (GO) has been studied in this work. X-ray diffraction, X-ray photoelectron spectroscopy, Fourier-transform infrared spectrometer, and atomic force spectroscopy were used to characterize GO. The results indicated that the adsorption followed the Freundlich model could be well described by pseudo-second order kinetic model. The adsorption capacity was much bigger than activated carbon and many natural clay minerals. The adsorption process was endothermic, and the adsorption mechanism of CTAB onto GO was proven to be controlled by surface complexation, hydrogen bonding, and electrostatic attraction.     

Self-assembly of cetyl trimethylammonium bromide in ethanol-water mixtures

The critical micelle concentration (CMC) of cetyl trimethylammonium bromide (CTAB) in both water and ethanol-water-mixed solvent was determined using steady-state fluorescence techniques in order to investigate the effect of the self-assembling properties of the surfactant on the template synthesis of porous inorganic materials. Results indicated that the CMC increased with the increase of ethanol concentration in the mixed solvent. The CMC of CTAB is 0.0009 mol/L in water, while it is 0.24 mol/L in ethanol. Furthermore, the dissipative particle dynamics (DPD) was adopted to simulate the aggregation of CTAB in water and ethanol/water mixtures, and the energy difference was calculated for the surfactant tail groups after mixing with the solvent. The simulation results reflected a regularity similar to the experimental data, i.e., tail groups of CTAB interacted more strongly with ethanol than with groups of CTAB interacted more strongly with ethanol than with water, which elucidates the reason that the micelle is difficult to form in ethanol. __________ Translated from Journal of Tianjin University, 2006, 39(1) (in Chinese)     

有机分子CTAB对银纳米颗粒形貌的影响

报道了一种有效调节银纳米颗粒形貌的特殊方法.在不同浓度的CTAB有机分子作用下,片状三角形银纳米颗粒形貌发生改变,形成圆形和纺锤形等特殊形貌的银纳米片,研究了CTAB浓度对银纳米颗粒形貌的影响,从实验结果分析了银纳米颗粒形貌发生改变的主要因素.