Peptide-assisted synthesis of gold nanoparticles and their self-assembly

A novel gold nanoparticle-tripeptide (GNP-tripeptide) conjugate was prepared by peptide in-situ redox technique at ambient temperatureusing a newly designed tripeptide. This new tripeptide was nso designed that it has a C-terminus tyrosine residue, which reduced Au+3 to Au, and the terminally located free amino group was bound to the gold nanoparticle (GNP) surface resulting in highly stable Au colloids. The average diameter of the tripeptide-stabilized GNP is 8.7 +/- 2.3 nm. Tripeptide bound gold nanoparticles formed three-dimensional assemblies in the presence of an excess of similar or disimilar tripeptides. The aggregation of GNPs results in a red shift in the surface plasmon resonance from lambda max = 527 to 556 nm. The effect of the solvent, concentration, and nature of the tripeptides on the assembly process were investigated by TEM and UV-visible spectroscopy.     

Preparation of iron oxide nanoparticles by microwave synthesis and their characterization

In this study production of fine particle Fe2O3 via microwave processing of Fe(NO3)3.nH2O followed by low temperature annealing was reported. XRD was used to characterize the structural properties of nanoparticles. Approximate particle sizes were between 3-13 nm according to Scherrer's equation. Single point BET measurement results also show that samples have large surface area and they are nanometer sized particles. TEM study was conducted to examine the structure of the nanoparticles. TEM figure is in good agreement with the results obtained from Scherrer's equation using XRD spectra. In order to characterize the magnetic properties of the nanoparticles VSM (Vibrating Sample Magnetometer) was used. From these results it can be concluded that the sample containing only maghemite phase exhibits superparamagnetic behaviour, on the other hand sample containing both hematite and maghemite phases shows paramagnetic behaviour above 300 K, superparamagnetic behavior at lower temperatures.     

Flower-shaped gold nanoparticles: synthesis, characterization and their application as SERS-active tags inside living cells

The detection of Raman signals inside living cells is a topic of great interest in the study of cell biology mechanisms and for diagnostic and therapeutic applications. This work presents the synthesis and characterization of flower-shaped gold nanoparticles and demonstrates their applicability as SERS-active tags for cellular spectral detection. The particles were synthesized by a facile, rapid new route that uses ascorbic acid as a reducing agent of gold salt. Two triarylmethane dyes which are widely used as biological stains, namely malachite green oxalate and basic fuchsin, were used as Raman-active molecules and the polymer mPEG-SH as capping material. The as-prepared SERS-active nanoparticles were tested on a human retinal pigment epithelial cell line and found to present a low level of cytotoxicity and high chemical stability together with SERS sensitivity down to picomolar particle concentrations.     

Nanostructure characterization of polymer-stabilized gold nanoparticles and nanofilms derived from green synthesis

The fabrication and characterization of gold (Au) nanostructured materials draws significant attention because of their distinctive properties and their technological applications. The first objective of this study is to fabricate polymer-stabilized Au nanoparticles and nanofilms (PAN) through a cost effective and green synthetic methodology. In this study, the gold trication (Au³⁺) can be spontaneously converted into metallic gold atom using a non-toxic reductant (ascorbic acid). The ultrafine Au clusters were formed and stabilized through metallic bonds in the colloidal suspension, which was then deposited on a micro-glass or polymer-bead substrate to prepare thin films. It was found that ascorbic acid was the best reducing agent due to its rapid rate, spontaneity of reaction, and its non-toxic nature. In order to prevent aggregation of the nanoparticles, a dispersing agent (gum Arabic) was used. The second objective of this study was to analyze the PAN using a number of state-of-the-art instrumentation techniques and analytical approaches, such as X-ray powder diffraction (XRD), atomic force microscopy (AFM), scanning and transmission electron microscopy (SEM and TEM), ultraviolet–visible (UV–Vis) spectroscopy, and ZetaPALS. These techniques were applied to evaluate specific properties of the PAN, such as characterization of its crystalline phase, surface topology, characteristic plasmon, particle size distribution, and stability. From this study, it can be concluded that the ultrafine Au nanoparticles and uniform films were obtained using the green chemistry method. The ultrafine Au particles are highly stabilized and monodispersed as demonstrated by their high absolute value of zeta potential.     

Facile synthesis of magnetic iron oxide nanoparticles and their characterization

Magnetic iron oxide nanoparticles are synthesized by suitable modification of the standard synthetic procedure without use of inert atmosphere and at room temperature. The facile synthesis procedure can be easily scaled up and is of important from industrial point of view for the commercial large scale production of magnetic iron oxide nanoparticles. The synthesized nanoparticles were characterized by thermal, dynamic light scattering, scanning electron microscopy and transmission electron microscopy analyses.     

Preparation of thermosensitive gold nanoparticles by plasma pretreatment and UV grafted polymerization

This work is to develop an easy method of plasma treatment and graft polymerization to prepare thermosensitive gold nanoparticles. Gold nanoparticles (Nano-Au) were reduced by trisodium citrate combined with hydrogen tetrachloroaurate(III) tetrahydrate (chloroauric acid) and modified with 11-mercaptoundecanoic acid (MUA) by the self-assembly monolayers (SAM). The surface graft polymerization of N-isopropylacrylamide (NIPAAm) was carried out by two steps, using O₂ plasma pretreatment of the surface on MUA SAM modified Nano-Au to form the peroxide groups on Nano-Au(MUA), and then subsequently using UV light to induce grafting with thermosensitive polymer. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to direct investigation of the particle size and morphology in situ. The diameters of the gold nanoparticles measured from the TEM images are in good agreement with data measured at room temperature which is about 15 nm. The thermosensitive gold nanoparticles were characterized by chemical structure of surface (ESCA) and Fourier-transform infrared spectroscopy (FTIR). ESCA result suggests that plasma treatments can be employed to generate peroxides on the Nano-Au(MUA) for the subsequent UV graft polymerization of PNIPAAm.     

Biological synthesis and characterization of intracellular gold nanoparticles using biomass of Aspergillus fumigatus

Nanotechnology is emerging as one of the most important and revolutionizing area in research field. Nanoparticles are produced by various methods like physical, chemical, mechanical and biological. Biological methods of reduction of metal ions using plants or microorganisms are often preferred because they are clean, non-toxic, safe, biocompatible and environmentally acceptable. In the present study, Aspergillus fumigatus was used for the intracellular synthesis of gold nanoparticles. Stable nanoparticles were produced when an aqueous solution of chloroauric acid (HAuCl₄) was reduced by A. fumigatus biomass as the reducing agent. Production of nanoparticles was confirmed by the colour change from yellow to pinkish violet after ～ 72 h of reaction. The produced nanoparticles were then characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction spectroscopy (XRD). SEM images of sample revealed that the nanoparticles were spherical, irregularly shaped with indefinite morphology. Biosynthesized gold nanoparticles were in the range of 85·1–210 nm in size. The presence of gold nanoparticle was confirmed by EDS analysis. Crystalline nature and face-centred cubic structure of synthesized gold nanoparticle was confirmed by XRD pattern.     

Controlled synthesis of gold nanoparticles by fluorescent light irradiation

A novel photochemical synthesis of size-controlled gold nanoparticles was reliably accomplished via both a direct reduction and a seeded-growth method at room temperature under the irradiation of fluorescent light. These methods utilized the intensity of fluorescent light that closely resembles daily sunlight (～100 mW cm(-2)). This effectively allowed for the formation of gold nanoparticles with tunable sizes simply by controlling the concentration of trisodium citrate and gold chloride. The broad band fluorescent light was found to be an efficient source for inducing the formation of gold nanoparticles at ambient conditions. The size distribution and absorption property of the resulting nanoparticles were thoroughly characterized by scanning/transmission electron microscopy, dynamic light scattering, UV-visible spectroscopy and powder x-ray diffraction. This photochemical synthesis demonstrates, for the first time, the reliable preparation of gold nanoparticles at room temperature upon irradiation with fluorescent light.     

Size-controlled synthesis of dendrimer-protected gold nanoparticles by microwave radiation

Well-stable dendrimer-protected gold nanoparticles were synthesized by microwave radiation of a third-generation poly(propyleneimine) dendrimer (PPI G3)–HAuCl₄ aqueous solution without the additional step of introducing other reducing agents and protective agents. The size of these gold nanoparticles thus formed can be controlled by molar ratio of dendrimer to gold.     

Phospholipid-assisted synthesis of size-controlled gold nanoparticles

Morphology and size control of gold nanoparticles (AuNPs) by phospholipids (PLs) has been reported. It was found that gold entities could form nanostructures with different sizes controlled by PLs in an aqueous solution. During the preparation of 1.5 nm gold seeds, AuNPs were obtained from the reduction of gold complex by sodium borohydride and capped by citrate for stabilization. With the different ratios between seed solution and growth solution, which was composed by gold complex and PLs, gold seeds grew into larger nanoparticles step by step until enough large size up to 30 nm. The main discovery of this work is that common biomolecules, such as PLs can be used to control nanoparticle size. This conclusion has been confirmed by transmission electron micrographs, particle size analysis, and UV-vis spectra.     

Photochemical synthesis of colloidal gold nanoparticles

Monodisperse gold nanoparticles protected by small organic molecules or by macromolecules with different sizes and shapes are widely used as a precursor material in various applications of gold nanotechnology. However, their preparation is still a formidable task. In this paper the use of photochemically assisted syntheses of monodisperse gold nanoparticles is summarized and some preparations by the authors’ group are introduced. These include spherical and rod-like particles, bimetallic composite nanoparticles, and syntheses using complex intramolecular photoreduction to generate the reducing agent.     

Microwave green synthesis of PVP-stabilised gold nanoparticles and their adsorption behaviour for methyl orange

In this work, gold nanoparticles (AuNPs) were prepared by the microwave irradiation method and comparative studies on the removal of dye by adsorption on activated carbon (AC) and polyvinylpyrrolidone (PVP)-supported AuNPs-coated AC were made. The uniform and stable AuNPs were prepared by the reduction of gold chloride (HAuCl₄) using glucose as reducing agent and PVP as a stabilising and capping agent. The resulting AuNPs were characterised by transmission electron microscopy (TEM) and UV-Vis spectroscopy. The TEM technique showed the presence of AuNPs with an average size of 20?nm. The effect of various process parameters has been investigated by following the column adsorption technique at room temperature. Percentage removal of dye increased with the decrease in initial concentration and increased with the increase in contact time. Adsorption data were modelled with the Freundlich isotherms. The Freundlich isotherm model has been applied to the equilibrium adsorption data. Desorption studies were made to elucidate recovery of the adsorbate and adsorbent for the economic competitiveness of the removal system. The adsorption capacity of the water-desorbed adsorbate reduced from 97% to 60% for n?=?6 cycles.     

Correlating self-assembly of block copolymers for their application in synthesis of gold nanoparticles

We report the role of self-assembly of polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) block copolymers for the synthesis of gold nanoparticles from hydrogen tetrachloroaureate (III) hydrate (HAuCl4 x 3H2O) in aqueous solution. The synthesis has been carried out using three different block copolymers P85 [EO26PO39EO26], F88 [EO103PO39EO103] and P105 [EO37PO56EO37], which not only have varying molecular weight but also differ in hydrophobicity to hydrophilicity ratio. The formation of gold nanoparticles is confirmed by the UV-Visible Spectroscopy. Transmission electron microscopy (TEM) provides the sizes of the nanoparticles formed in these systems. Small-Angle Neutron Scattering (SANS) and Dynamic Light Scattering (DLS) techniques are used to correlate the self-assembly of block copolymer to their propensity to form gold nanoparticles. The yield is found to be in the order P105 > P85 > F88 and is related to the higher tendency of block copolymer to self-assemble to give greater yield of gold nanoparticles. For all the block copolymers, SANS and DLS results suggests that the yield in the synthesis does not always increases with the salt concentration and is limited due to the fact that most of the block copolymers remain unassociated with the gold nanoparticles. By making use of these unassociated block copolymers, we propose two methods (i) step addition method and (ii) additional reductant method, where the synthesis yield of gold nanoparticles can be enhanced by manifold.     

Microstructural characterization of gold nanoparticles synthesized by solution plasma processing

Microstructural characteristics of gold nanoparticles (Au NPs) fabricated by solution plasma processing (SPP) in reverse micelle solutions have been studied by high-resolution transmission electron microscopy (HRTEM). The synthesized Au NPs, with an average size of 6.3 ± 1.4?nm, have different crystal characteristics; fcc single-crystalline particles, multiply twinned particles (MTPs), and incomplete MTPs (single-nanotwinned fcc configuration). The crystal structure characteristics of the Au NPs synthesized by the SPP method were analyzed and compared with similar-size Au NPs obtained by the conventional chemical reduction synthesis (CRS) method. The TEM analysis results show that the Au NPs synthesized by the CRS method have shapes and crystal structures similar to those nanoparticles obtained by the SPP method. However, from the detailed HRTEM analysis, the relative number of the Au MTPs and incomplete MTPs to the total number of the Au NPs synthesized by the SPP method was observed to be around 94%, whereas the relative number of these kinds of crystal structures fabricated by the CRS method was about 63%. It is most likely that the enhanced formation of the Au MTPs is due to the fact that the SPP method generates highly reaction-activated species under low environmental temperature conditions.     

Sunlight-driving formation and characterization of size-controlled gold nanoparticles

Exposing a sodium citrate-HAuCl4 aqueous solution to sunlight results in the formation of size-controlled, citrate-capped gold nanoparticles. The gold nanoparticles were characterized by UV-visible, transmission electron microscopy (TEM), scanning electron microcopy (SEM), and X-ray diffraction (XRD) spectroscopic methods. It provides a general methodology for the economic, convenient, mild preparation of citrate-capped noble metal nanoparticles.     

Ionogel-templated synthesis and organization of anisotropic gold nanoparticles

Photochemical reduction of tetrachloroaurate (AuCl4-) ions in the highly constrained aqueous domains of a nanostructured ionogel template, formed via self-assembly of the ionic liquid 1-decyl-3-methylimidazolium chloride (C10mim+Cl-) in water, results in the formation of anisotropic gold nanoparticles with a variety of sizes and morphologies, which include previously unattainable trigonal prismatic nanorods. Unexpectedly, small-angle X-ray scattering studies of the Au-ionogel composite reveal that the in situ formation of the nanoparticles increases the mesoscopic order of the ionogel, which results in its conversion to a near-monodomain structure. The findings demonstrate that nanostructured, ionic liquid-based gels can be used to template the formation of new nanoparticle morphologies with technologically important optical, electronic, and catalytic properties. It may also be possible to design soft templates that permit the fabrication of highly ordered nanoparticle array-hydrogel composites, thereby enabling control and tuning of the collective properties of the encapsulated nanoparticles.     

Au/Ag芯-壳复合结构纳米颗粒的制备和表征

利用二步液相还原法制备了 Au/Ag 芯 壳复合结构的纳米颗粒。用 TEM对反应液中金离子和银离子的摩尔比分别为1∶2和1∶1时所制备的 Au/Ag芯 壳复合结构的纳米颗粒的尺寸和形貌进行了表征。其紫外 可见吸收光谱具有 2 个可区分的吸收带,与纯金和纯银纳米颗粒的光学吸收特性对比后认为:随着反应液中银离子摩尔份数的增加,等离子体共振吸收峰始终位于 410nm附近的吸收带为银纳米颗粒的等离子体吸收带;另一个将随之产生蓝移的吸收带为Au/Ag芯 壳复合结构纳米颗粒的等离子体吸收带,蓝移是由于银壳厚度的增加而引起的。     

Facile synthesis of chondroitin sulfate-stabilized gold nanoparticles

A facile and simple method for the synthesis of biocompatible gold nanoparticles (AuNPs) at room temperature has been developed by using sodium borohydride as the reducing agent and employing an inexpensive water-soluble chondroitin sulfate (CS) biopolymer as the stabilizing agent. The as-prepared AuNPs were characterized with ultraviolet–visible (UV–vis) spectroscopy and transmission electron microscopy (TEM). Additionally, the stability of AuNPs in aqueous solution was investigated as a function of the electrolyte sodium chloride concentration. The experimental results showed that even high sodium chloride concentration (1 M) also did not destabilize the colloidal gold solution. So it could be speculated that the high stability of AuNPs should be attributed to the electrostatic repulsion and steric hindrance between the AuNPs stabilized by CS molecules, which wrapped around the surface of as-prepared AuNPs and prevented their agglomeration, and simultaneously improve biocompatibility of AuNPs as well.     

Sonochemical synthesis of gold nanoparticles on chitosan

Au nanoparticles deposited on chitosan were readily prepared from aqueous solution of NaAuCl₄ containing chitosan powder by the reaction with sonochemically formed reducing species. The average size of the formed Au particles was measured to be 22 nm with a relatively narrow size distribution, although there was no specific stabilizer for Au nanoparticles.