Effects of polymer micelles of alkylated polyethylenimines on generation of gold nanoparticles

Mono- and di-alkylated polyethylenimines (PEI-1R, PEI-2R) were synthesized and used as both reductants, by exploiting the functionality of the polyethylenimine's (PEI) amino groups, and stabilizers able to protect nascent gold nanoparticles generated from hydrogen tetrachloroaurate (HAuCl4). From TEM images of the stained polymers, it is clear that the polymer micelles are round and well-structured when formed from PEI-2R, fused and less well-structured when formed from PEI-1R, and totally nonstructured when formed from PEI. These findings coincide with the results found by using pyrene as a probe to investigate aggregation behavior, where PEI-2R with a fluorescence intensity ratio (I1/I3) of 1.48 forms the more closely packed polymer micelles than PEI-1R (I1/I3 = 1.64) and PEI (I1/I3 = 1.72). The use of the highly alkylated polymer micelle (PEI-2R) results in the fastest reduction of HAuCl4, and gives the most effective protection to the generated gold nanoparticles. When used at higher polymer concentrations than required for micelle formation, it was found that polymer hydrophobicity was highly influential in directing the nanoparticle's morphology, i.e., the resulting polymer micelles were labeled with perfect and round necklace-like gold nanoparticles when PEI-2R was used, and imperfect and less round gold nanoparticles when PEI-1R was employed. These structures were totally absent when PEI was used. The use of alkylated PEI, being able to act simultaneously as both a reductant and as a very effective protective agent, greatly simplifies the process used for preparing gold nanoparticles.     

Preparation and encapsulation of highly fluorescent conjugated polymer nanoparticles

A facile method has been developed to prepare aqueous dispersions of encapsulated conjugated polymer nanoparticles exhibiting high fluorescence brightness. Salient features of the nanoparticles include their small diameter and spherical morphology. Encapsulation of the nanoparticles with a silica shell reduces the rate of photooxidation and allows facile attachment of functional groups for subsequent bioconjugation and nanoparticle assembly. Functionalization of the nanoparticle with amine groups followed by the addition of Au nanoparticles resulted in the formation of nanoparticle assemblies, as evidenced by the efficient quenching of the conjugated polymer fluorescence by the Au nanoparticles.     

Structural effects of amphiphilic block copolymers on the gold nanoplates synthesis. Experimental and theoretical study

Geometric and multi-arms gold nanoplates were synthesized by direct reaction between two different amphiphilic block copolymers and KAuCl₄ in aqueous solution. Amphiphilic copolymers containing blocks of ε-caprolactone and N-vinyl-2-pyrrolidone were used. The block copolymer structures and concentration play a key role on the morphology and size of gold nanoparticles. Copolymers have a dual function as reductant and stabilizer agent. The gold nanoparticles obtained were characterized by transmission electron microscopy (TEM), UV–visible spectroscopy (UV–vis) and dynamic light scattering (DLS). On the other hand, electronic structure calculations, based on density functional theory were performed to support the experimental results. The simple models built with small clusters of gold and co-monomer units provide planar structures complexes with higher stabilization energies. These results agree with the nanoplates obtained experimentally. Moreover, the reactivity analysis based on monoelectronic properties suggests that the formation of aggregates between complexes is favored.     

Optimization of high-yield biological synthesis of single-crystalline gold nanoplates

In this work, single-crystalline gold nanoplates were obtained by reducing aqueous chloroauric acid solution with the extract of Sargassum sp. (brown seaweed) at room temperature. The gold nanoplates so obtained were characterized by UV-vis spectroscopy, X-ray diffraction, atomic force microscopy, and transmission electron microscopy. The formation of gold nanoplates was found to depend on a number of environmental factors, such as the time taken to age the seaweed extract, pH of the reaction medium, reaction temperature, reaction time, and initial reactant concentrations. The size of the gold nanoplates could be controlled to between 200 and 800 nm by manipulating the initial reactant concentrations. The yield of the flat gold nanocrystals relative to the total number of nanoparticles formed was as high as approximately 80-90%.     

Thermal aqueous solution approach for the synthesis of triangular and hexagonal gold nanoplates with three different size ranges

The synthesis of gold nanoplates was carried out in an aqueous solution by thermal reduction of HAuCl(4) with trisodium citrate in the presence of cetyltrimethylammonium bromide (CTAB) surfactant in just 5-40 min. The sizes of the gold nanoplates can be varied from as small as tens of nanometers in width, to several hundreds of nanometers, and even a few microns in width by changing the reagent concentrations, solution temperature, and the reaction time. A [CTAB]/[HAuCl(4)] ratio of 6 in the reaction solution was found to be favorable for the formation of gold nanoplates. The nanoplates possess well-defined shapes with sharp edges. The small nanoplates exhibit mainly a triangular shape, while larger nanoplates show a mixture of triangular, hexagonal, truncated triangular, and other symmetrical structures. The nanoplates are composed of essentially (111) lattice planes, as revealed by both XRD and TEM results. Nanoplates with widths from several hundreds of nanometers to a few microns absorb light strongly in the near-infrared region. The growth mechanism of these nanoplates was investigated. The ability to synthesize gold nanoplates with these different size ranges in large scale in aqueous solution using simple CTAB capping surfactant should allow more diverse applications of gold nanoplates.     

Poly(ethyleneimine) as reducing and stabilizing agent for the formation of gold nanoparticles in w/o microemulsions

This paper is focused on the use of branched poly(ethyleneimine) (PEI) as reducing as well as stabilizing agent for the formation of gold nanoparticles in different media. The process of nanoparticle formation was investigated, in the absence of any other reducing agents, in microemulsion template phase in comparison to the nucleation process in aqueous polymer solution.

On the one hand, it was shown that the polyelectrolyte can be used for the controlled single-step synthesis and stabilization of gold nanoparticles via a nucleation reaction and particles with an average diameter of 7.1 nm can be produced.

On the other hand, it was demonstrated that the polymer can also act as reducing and stabilizing agent in much more complex systems, i.e. in water-in-oil (w/o) microemulsion droplets. The reverse microemulsion droplets of the quaternary system sodium dodecylsulfate (SDS)/toluene–pentanol (1:1)/water were successfully used for the synthesis of gold nanoparticles. The polymer, incorporated in the droplets, exhibits reducing properties, adsorbs on the surface of the nanoparticles and prevents their aggregation. Consequently, nanoparticles of 8.6 nm can be redispersed after solvent evaporation without a change of their size.

Nevertheless, the polymer acts already as a “template” during the formation of the nanoparticles in water and in microemulsion, so that an additional template effect of the microemulsion is not observed.

The particle formation for both methods is checked by means of UV–vis spectroscopy and the particle size and size distribution are investigated via dynamic light scattering and transmission electron microscopy (TEM).     

Simple reductant concentration-dependent shape control of polyhedral gold nanoparticles and their plasmonic properties

We report a facile seed-mediated method for the synthesis of monodisperse polyhedral gold nanoparticles, with systematic shape evolution from octahedral to trisoctahedral structures. The control over the particle growth process was achieved simply by changing the concentration of the reductant in the growth solution, in the presence of small spherical seed nanoparticles. By progressively increasing the concentration of the reductant used in the growth solution (ascorbic acid), while keeping the amount and type of added surfactant constant, the morphology of the gold nanoparticles was varied from octahedral to truncated octahedral, cuboctahedral, truncated cubic, cubic, and finally trisoctahedral structures. These nanoparticles were monodisperse in size, possessed similar volumes, and were naturally oriented so that their larger crystal planes were face down on quartz substrates when deposited from the solution. By adjusting the volume of gold seed nanoparticle solution added to a growth solution, the size of the simplest gold nanoparticles (with a highly symmetric cubic morphology) could be tuned from 50 ± 2.1 to 112 ± 11 nm. When other seed nanoparticles were used, the size of the cubic Au nanoparticles reached 169 ± 7.0 nm. The nanoparticle growth mechanism and the plasmonic properties of the resulting polyhedral nanoparticles are discussed in this paper.     

Photochemical synthesis of gold nanoparticles in aqueous dispersions of carboxylated polystyrene

Photochemical synthesis of gold nanoparticles in aqueous dispersions of carboxylated polystyrene with microsphere sizes of 100, 300, 500, and 1410 nm under the action of monochromatic light with an excitation wavelength of 254 nm was studied. Preliminary irradiation of the polymer dispersion induces formation of gold particles under dark conditions. Dependences of gold nanoparticles formation on the duration of preliminary polymer irradiation and concentration of introduced HAuCl₄ aqueous solution were determined. A mechanism of the polystyrene-assisted formation of gold nanoparticles was proposed. The size and structure of gold nanoparticles were determined.     

High-yield synthesis of large single-crystalline gold nanoplates through a polyamine process

A polyamine process has been demonstrated for the high-yield preparation of single-crystalline gold nanoplates with several 10 microm in size, carried out by heating a concentrated aqueous solution of linear polyethylenimine and HAuCl4 at 100 degrees C. It suggests that the concentration of reactants is crucial to the formation of nanoplates.     

Shape-controlled synthesis of gold icosahedra and nanoplates using Pluronic P123 block copolymer and sodium chloride

Gold icosahedra with an average diameter of about 600 nm were easily prepared by heating an aqueous solution of the amphiphilic block copolymer, poly(ethylene oxide)₂₀-poly(propylene oxide)₇₀-poly(ethylene oxide)₂₀ (Pluronic P123), and hydrogen tetrachloroaurate(III) trihydrate (HAuCl₄·3H₂O) at 60 °C for 25 min. When sodium chloride (NaCl:HAuCl₄ molar ratio=10:1) was added to this aqueous solution, gold nanoplates were produced. The chloride ion was found to be a key component in the formation of the gold nanoplates by facilitating the growth of {111} oriented hexagonal/triangular gold nanoplates, because similar gold nanoplates were produced when LiCl or KCl was added to the aqueous solution instead of NaCl, while gold nanocrystals having irregular shapes were produced when NaBr or NaI was added.     

MC8 Peptide-Mediated Her-2 Receptor Targeting Based on PEI-β-CyD as Gene Delivery Vector

A novel vector with high gene delivery efficiency and special cell targeting ability was developed using a good strategy that utilized low molecular weight polyethylenimine (PEI; molecular weight, 600 KDa [PEI600]) cross-linked to β-cyclodextrin (β-CyD) via a facile synthetic route. Human epidermal growth factor receptor 2 (Her-2) are highly expressed in a variety of human cancer cells and are potential targets for cancer therapy. MC8 peptides, which have been proven to combine especially with Her-2 on cell membranes were coupled to PEI-β-CyD using N-succinimidyl-3-(2-pyridyldithio) propionate as a linker. The ratios of PEI600, β-CyD, and peptide were calculated based on proton integral values obtained from the ¹H-NMR spectra of the resulting products. Electron microscope observations showed that MC8-PEI-β-CyD can efficiently condense plasmid DNA (pDNA) into nanoparticles of about 200 nm, and MTT assays suggested the decreased toxicity of the polymer. Experiments on gene delivery efficiency in vitro showed that MC8-PEI-β-CyD/pDNA polyplexes had significantly greater transgene activities than PEI-β-CyD/pDNA in the Skov3 and A549 cells, which positively expressed Her-2, whereas, no such effect was observed in the MCF-7 cells, which negatively expressed Her-2. Our current research indicated that the synthesized nonviral vector shows improved gene delivery efficiency and targeting specificity in Her-2 positive cells.     

Some physico-chemical properties and sorption ability of benzylated polyethyleneimines in aqueous solutions

An investigation has been made on the change in the physico-chemical properties of aqueous solutions of branched and linear polyethyleneimine (a high mol. wt catalyst for hydrolysis of nitrophenyl esters) occurring on its being alkylated by benzyl chloride. The first result of alkylation is benzyldiethylamine fragments in PEI. Provided that the degree of conversion is below 0–3, the reaction is second order. Then the rate constant decreases, probably due to a decrease in the steric factor. Alkylation diminishes pK_a's of nitrogen atoms of PEI. Accumulation of benzyl groups in PEI results in a marked contraction of its macromolecules in aqueous solutions and enhances the sorption ability with respect to n-nitroanilides. The free energy of sorption is ?4 · 1 to ? 5·5 kcal/mole.     

Formation of gold nanoparticles catalyzed by platinum nanoparticles: assessment of the catalytic mechanism

The understanding of how the formation of metal nanoparticles in aqueous solutions is influenced by the presence of presynthesized nanoparticles is important for precise control over size, shape, and composition of nanoparticles. New insights into the catalytic mechanism of Pt nanoparticles are gained by studying the formation of gold nanoparticles from the reduction of AuCl(4)(-) in aqueous solution in the presence of presynthesized Pt nanoparticles as a model system. The measurement of changes of the surface plasmon resonance band of gold nanoparticles, along with TEM analysis of particle size and morphology, provided an important means for assessing the reaction kinetics. The reductive mediation of Pt-H species on the Pt nanocrystal surface is believed to play an important role in the Pt-catalyzed formation of gold nanoparticles. This important physical insight is evidenced by comparison of the rates of the Pt-catalyzed formation of gold nanoparticles in the presence and in the absence of hydrogen (H(2)), which adsorb dissociatively on a Pt nanocrystal surface forming Pt-H species. Pt-H effectively mediates the reduction of AuCl(4)(-) toward the formation of gold nanoparticles. Implications of the findings to the controllability over size, composition, and morphology of metal nanoparticles in the aqueous synthesis environment are also discussed.     

Silver nanoplates formed at the air/water and solid/water interfaces

Silver nanoparticles and nanoplates were prepared at the air/AgNO₃ aqueous solution interfaces under poly(9-vinylcarbazole) (PVK) monolayers when illuminated by UV-light at room temperature and elevated temperatures, respectively. When the illuminated films at the air/water interfaces were covered by carbon-coated copper grids, nanoplates were formed even at room temperature, and the size of the nanoplates was much larger than those formed at the air/water interface under the same experimental conditions, indicating that copper took part in the formation of Ag nanoplates through the galvanic displacement reaction between Cu and Ag⁺ ions with the help of carbon layer to conduct electrons. It was found that the basal plane of these nanoplates is the (1 1 1) face of a face-centered cubic (fcc) Ag crystal. Although platelike structure can be formed at the carbon-coated copper grid/AgNO₃ aqueous solution interface without PVK film, it shows different features from those with PVK films, indicating that PVK film plays an important role in the formation of regular large nanoplates. Further observations indicate that special restrained microenvironment, adsorption of PVK molecules on a specific crystal face, anisotropic growth and attachment of the nanoparticles are responsible for the formation of the nanoplates.     

In situ formation and size control of gold nanoparticles into chitosan for nanocomposite surfaces with tailored wettability

The in situ formation of gold nanoparticles into the natural polymer chitosan is described upon pulsed laser irradiation. In particular, hydrogel-type films of chitosan get loaded with the gold precursor, chloroauric acid salt (HAuCl(4)), by immersion in its aqueous solution. After the irradiation of this system with increasing number of ultraviolet laser pulses, we observe the formation of gold nanoparticles with increasing density and decreasing size. Analytical studies using absorption measurements, atomic force microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy of the nanocomposite samples throughout the irradiation procedure reveal that under the specific irradiation conditions there are two competing mechanisms responsible for the nanoparticles production: the photoreduction of the precursor responsible for the rising growth of gold particles with increasing size and the subsequent photofragmentation of these particles into smaller ones. The described method allows the localized formation of gold nanoparticles into specific areas of the polymeric films, expanding its potential applications due to its patterning capability. The size and density control of the gold nanoparticles, obtained by the accurate increase of the laser irradiation time, is accompanied by the simultaneously controlled increase of the wettability of the obtained gold nanocomposite surfaces. The capability of tailoring the hydrophilicity of nanocomposite materials based on natural polymer and biocompatible gold nanoparticles provides new potentialities in microfluidics or lab on chip devices for blood analysis or drugs transport, as well as in scaffold development for preferential cells growth.     

新形金纳米片的简单制备与生长机制

在室温(~30 ℃)条件下,氯金酸(HAuCl₄)均匀混合在粘稠的表面活性剂聚乙烯吡咯烷酮(PVP)胶体(水为溶剂)中,HAuCl₄可以被PVP还原,从而形成纳米片. 本工作中,通过调整晶体生长条件,成功合成了大量新形貌的单晶金纳米片(厚度数十纳米,尺寸为数个微米). 例如,在晶体生长初期阶段,通过引入温度变化(如降温10-20 ℃),形成的金纳米片主要是六角星形,并伴有盾状、内凹外凸的三角状、截角的、三叉的及多台阶等新形纳米片. 结合理论计算,阐明了金纳米片的生长机制：在一定条件下,金(111)晶面不仅可以沿着<110>方向生长成为常规的三角或六角纳米片,还可以沿<211>、<321>等不同方向生长成含有更高指数侧面的新形金纳米片.     

Controlled Synthesis of CdClOH Sub-nanocones by Low-temperature Solution Process and Their Transformation into CdS Hollow Sub-nanocones

Novel CdClOH sub‐nanocone crystals were successfully synthesized on a large scale by a facile solution‐based method using polymers as crystal growth modifiers. The crystals showed cone‐like morphology. Some factors affecting the morphology and size of the product, such as reaction temperature, concentrations of polyacrylamide (PAM), and pH value of the solution, were systematically studied. Experiments implied that polymer PAM played a key role in the formation of CdClOH sub‐nanocones. A possible formation mechanism of CdClOH sub‐nanocones was suggested based on nucleation‐etching process‐recrystallization in a mild aqueous solution. Furthermore, the as‐prepared CdClOH sub‐nanocones could be further transformed into CdS hollow sub‐nanocones by an anion‐exchange reaction.     

Facile Synthesis of Porous Mn2O3 Nanoplates and Their Electrochemical Behavior as Anode Materials for Lithium Ion Batteries

Porous Mn₂O₃ nanoplates were prepared by a facile polyol solution method combined with a simple post‐annealing process. The porous Mn₂O₃ nanoplates were characterized by XRD, field‐emission SEM, high‐resolution TEM, and N₂ adsorption/desorption isotherm measurements. The formation process for the Mn₂O₃ nanoplates was proposed as a morphology‐conserved transformation strategy. These porous nanoplates exhibited improved electrochemical performance with excellent cycling stability and good rate capability when applied as anode materials in lithium ion batteries.     

Enhanced hydrolytic stability of self-assembling alkylated two-dimensional covalent organic frameworks

The stability and bulk properties of two-dimensional boronate ester-linked covalent organic frameworks (COFs) were investigated upon exposure to aqueous environments. Enhanced stability was observed for frameworks with alkylation in the pores of the COF compared to nonalkylated, bare-pore frameworks. COF-18? and COF-5 were analyzed as "bare-pore" COFs, while COF-16? (methyl), COF-14? (ethyl), and COF-11? (propyl) were evaluated as "alkylated-pore" materials. Upon submersion in aqueous media, the porosity of alkylated COFs decreased ～25%, while the nonalkylated COFs were almost completely hydrolyzed, virtually losing all porosity. Similar trends were observed for the degree of crystallinity for these materials, with ～40% decrease for alkylated COFs and 95% decrease for nonalkylated COFs. SEM was used to probe the particle size and morphology for these hydrolyzed materials. Stability tests, using absorbance spectroscopy and (1)H NMR, monitored the release of monomers as the COF degraded. While nonalkylated COFs were stable in organic solvent, hydrolysis was rapid in aqueous environments, more so in basic compared to neutral or acidic aqueous media (minutes to hours, respectively). Notably, alkylation in the pores of COFs slows hydrolysis, exhibiting up to a 50-fold enhancement in stability for COF-11? over COF-18?.     

Surface plasmon modes of gold nanospheres, nanorods, and nanoplates in an organic solvent: phase-transfer from aqueous to organic media

We present a process for the phase-transfer of gold nanoparticles from an aqueous to an organic medium with normal alkanethiols. This method can be applied not only to large nanospheres (d~100 nm) but also to anisotropic nanoparticles like nanorods and nanoplates. It allows the comparison of the nanoparticle optical properties when they are dispersed in both aqueous and organic media.